IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 50, NO. 1, JANUARY 2014 7

High Performance InAs/In0.53Ga0.23Al0.24As/InPQuantum Dot 1.55 μm Tunnel Injection Laser

Sishir Bhowmick, Md Zunaid Baten, Thomas Frost, Boon S. Ooi, Senior Member, IEEE,and Pallab Bhattacharya, Fellow, IEEE

Abstract— The characteristics of 1.55 μm InAs self-organizedquantum-dot lasers, grown on (001) InP substrates by molecularbeam epitaxy, have been investigated. Modulation doping of thedots with holes and tunnel injection of electrons have beenincorporated in the design of the active (gain) region of thelaser heterostructure. Large values of To = 227 K (5 °C ≤ T ≤45 °C) and 100 K (45 °C < T ≤ 75 °C) were derived fromtemperature dependent measurements of the light-current char-acteristics. The modal gain per dot layer is 14.5 cm−1 and thedifferential gain derived from both light-current and small-signalmodulation measurements is ∼0.8 × 10−15 cm2. The maximummeasured −3 dB small-signal modulation bandwidth is 14.4 GHzand the gain compression factor is 5.4 × 10−17 cm2. The lasersare characterized by a chirp of 0.6 Å for a modulation frequencyof 10 GHz and a near zero α-parameter at the peak of the laseremission. These characteristics are amongst the best from any1.55 μm edge-emitting semiconductor laser.

Index Terms— Quantum dot laser, molecular beam epitaxy,tunnel injection, small-signal characteristics, differential gain.

I. INTRODUCTION

THE light source that serves as the workhorse inlong-haul optical communication links is a 1.55 μm

laser, to take advantage of the minimum fiber attenu-ation in this wavelength range. These long wavelengthedge-emitting lasers are generally InP-based and the active(gain) region is lattice-matched In0.53Ga0.47As/InGaAsP/InPor In0.53Ga0.47As/InGaAlAs/In0.52Al0.48As double hetero-structure or multi-quantum wells (MQWs) [1]-[5]. Pseudo-morphic or strain-compensated QWs are also used to engineerthe gain, confinement energies and associated characteristics[6]-[8]. Because of the small bandgap, of the gain regioninjected carriers undergo Auger recombination which,together with lower gain and differential gain, compared tolarge bandgap devices, lead to larger threshold currents, large

Manuscript received August 23, 2013; revised November 4, 2013; acceptedNovember 11, 2013. Date of publication November 14, 2013; date of currentversion November 20, 2013. The work was supported by the King AbdullahUniversity of Science and Technology, Kingdom of Saudi Arabia, under GrantCRG-1-2012-001-010-MIC.

S. Bhowmick, M. Z. Baten, T. Frost, and P. Bhattacharya are with theCenter for Nanoscale Photonics and Spintronics, Department of ElectricalEngineering and Computer Science, University of Michigan, Ann Arbor,MI 48109-2122 USA (e-mail: sishir@umich.edu; mdzunaid@umich.edu;tfrost@umich.edu; pkb@eecs.umich.edu).

B. S. Ooi is with the Photonics Laboratory, King Abdullah Univer-sity of Science and Technology, Thuwal 21534, Saudi Arabia (e-mail:boon.ooi@kaust.edu.sa).

Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JQE.2013.2290943

temperature dependence of the threshold current (small To),and large chirp and α-factor associated with small-signalmodulation.

GaAs-based quantum dot lasers incorporating multiple self-organized In(Ga)As/GaAs quantum dot (QD) layers havedemonstrated superior performance at 1.3 μm [9]-[15], result-ing from the large gain and differential gain in the dots andmore optimized carrier confinement compared to quantum welllasers. The lasers are characterized by To ∼ ∞, extremely lowthreshold current, large small-signal modulation bandwidthof ∼15 GHz, and near-zero chirp and α-factor [9]-[15].Unfortunately, the emission wavelength of these lasers cannotbe extended to 1.55 μm without the use of metamorphic bufferlayers, which degrade device performance due to the presenceof mismatch defects.

There have been reports on InP-based semiconductor lasersthat incorporate self-organized InAs quantum dashes as activeregions [16]-[23]. Under group V stabilized surface conditions,the quantum dashes are typically elongated along the [110]direction on (001) InP substrates due to longer indium surfacediffusion length along this direction [16], [17]. The emissionwavelength of the quantum dashes can be readily tuned in thespectral range of 1.2 to 2.0 μm. Self-organized InAs quantumdashes typically exhibit characteristics similar to InAs/GaAsquantum dots in the transverse direction and therefore strongquantum confinement can be achieved. In the longitudinaldirection, the quantum dashes are more than 100 nm long,which results in very weak quantum confinement. InAs quan-tum dashes exhibit closely spaced electron and hole energylevels and a large Auger recombination rate, which oftenseverely limit the performance of the lasers. Additionally,the achievement of high quality quantum dashes, with smallinhomogeneous broadening of the luminescence spectrum, isstill elusive due to the complex interplay of thermodynam-ics and surface kinetics at the growth front of InAlGaAslayers. While many groups have reported the growth andcharacteristics of quantum dash lasers, failure to address theseproblems generally leads to devices with poor performanceat room temperature, such as very large threshold current,highly temperature sensitive operation (To ∼50-90 K) [20],[24]-[26] large linewidth enhancement factor (≥2) [26] andlow modulation bandwidth (≤7 GHz) [21].

Three-dimensional InAs/InGaAlAs/InP quantum dots havebeen recently grown by molecular beam epitaxy (MBE) inthe Stranski-Krastanow mode using an As2 source [27] and1.55 μm edge-emitting and distributed feedback (DFB) QD

0018-9197 © 2013 IEEE

8 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 50, NO. 1, JANUARY 2014

lasers have been reported [28]-[30]. However, the fact remainsthat we are dealing with lasers having small-bandgap materialsin the active region and hence Auger recombination andrelated hot-carrier effects are bound to play a significant role.Tunnel injection of carriers into the active region has beenused with great success to minimize hot carrier effects inquantum well and quantum dot lasers [7], [8], [11], [13],[14], [31]. In the most commonly used scheme, cold electronsare directly injected from a wide injector region through abarrier into the ground or first excited state of quantum wellsor dots by resonant direct or non-resonant phonon-assistedtunneling [11], [13], [14]. Hot carrier effects resulting fromthe large two-dimensional density of states in the dot wettinglayer and barrier regions and carrier leakage are minimized,resulting in devices with increased differential gain, reducedgain compression, high To, and reduced α-parameter and chirp[13], [14]. It is also well-recognized that the hole distributionin quantum dots is thermally broadened into many availablestates with very small energy spacing and therefore a largeinjected carrier density would be required for large gain inthe ground state. With acceptor (p) doping, extra holes areprovided at the ground state energy by either direct doping ofthe dots or by modulation doping in the barriers [10], [12].Such doping is also known to reduce hot carrier effects.

In the present study, we have incorporated the electron tun-nel injection scheme and modulation doping of the dots withholes in the design of InAs/InGaAlAs/InP QD lasers grown byMBE. Both broad-area and near-single mode ridge waveguideedge-emitting lasers have been fabricated and their static anddynamic characteristics have been measured. The lasers arecharacterized by large differential gain (0.8 × 10−15 cm2),relatively low threshold current density (390 A/cm2), verylarge To (227 K in the range 5 °C ≤ T ≤ 45 °C and 100 K in45 °C ≤ T ≤ 75 °C), large modulation bandwidth (14.4 GHz)and low α-parameter (0.17) and chirp (0.6Å), making themextremely attractive for long-haul fiber-optic communicationlinks.

II. EPITAXIAL GROWTH AND FABRICATION OF QD LASERS

The MBE growth of self-organized InAs/InGaAlAs/InPquantum dots is first described. InAs quantum dots are grownon a In0.53Ga0.23Al0.24As layer lattice matched to InP substrateby depositing 5 monolayers of InAs at an optimized temper-ature of 495 °C under As2 flux with a V/III ratio of 18. Thegrowth rate of InAs is kept fixed at 360 nm/hr. An ultra-thin5Å GaAs layer is grown on In0.53Ga0.23Al0.24As just prior tothe growth of quantum dots, which we believe reduces thesurface roughness of the In0.53Ga0.23Al0.24As layer, increasesthe In adatom mobility on the surface and therefore helps toincrease dot density and size uniformity. The areal density ofquantum dots measured by atomic force microscopy (AFM)(Fig. 1) is ∼5 × 1010 cm−2, which is quite high for thismaterial system. The average dot diameter is ∼25 nm andheight is ∼5-6 nm. The very tall features observed in the AFMimage are consequences of the initial surface roughness, whichprovides disordering of the nucleation centers for the growthof the QDs, leading to coalescing of individual dots [32].

Fig. 1. Atomic force microscopy (AFM) image of InAs/In0.53Ga0.23Al0.24As/InP quantum dots grown by molecular beam epitaxy. The dot densityis estimated to be 5 × 1010 cm−2.

This, in effect, results in the creation of dislocations due tothe coalesced dots being relaxed. Hence it is expected thatfurther optimization of the growth process can reduce thedefect density and further enhance device performance.

The band diagram of the tunnel heterostructure and theelectronic states in the quantum dot are obtained by solvingthe Schrödinger equation. The final design is obtained by finetuning with photoluminescence (PL) measurements on controlsamples. The bandgap in the injector well and dot regionsnecessitate phonon-assisted non-resonant tunneling into thedot ground state. The InAs tunnel injection quantum-dot laserheterostructure, as shown in Fig. 2(a), is grown on Si-doped(001)InP susbstrates. The n- and p-cladding layers consistingof 0.8 μm In0.52Al0.48As:Si and 1.0 μm In0.52Al0.48As:Be,respectively, are grown at an optimized temperature of 515 °Cat a rate of 0.72 μm/hr. The active region consisting of fiveperiods of injector well and dot tunnel injection heterostruc-tures, separated by 40 nm In0.53Ga0.23Al0.24As barriers, aregrown at 495 °C. In each period, an 8 nm In0.45Ga0.55As quan-tum well is grown as the injector region. The injector well andquantum dot layer are separated by a 2.5 nm In0.52Al0.48Astunnel barrier. The PL emissions of both the well and dotlayers are carefully tuned so that the ground state of thewell is approximately one optical phonon energy (∼36 meV)above the ground state of the dot layer. The quantum dots aremodulation doped p-type with a 10 nm Be-doped (p = 4.0 ×1011 cm−2) region in the In0.53Ga0.23Al0.24As barriers. Themode profile in the waveguide was calculated (Fig. 2(b)) anda mode confinement factor of � = 0.03 is derived. The roomtemperature PL spectrum is shown in Fig. 3(a), where emissionfrom the injector well and dot layers peak at 1.505 μm and1.577 μm, respectively, and the full-width-at-half-maximum(FWHM) of the quantum dot emission is ∼32 meV.

Both broad area (50 μm wide and 390-2000 μm long) andridge waveguide (2-4 μm wide and 390-2000 μm long) edgeemitting lasers were fabricated by standard photolithographyand wet etching and contact metallization techniques. The laserfacets obtained by cleaving were left uncoated.

BHOWMICK et al.: HIGH PERFORMANCE InAs/In0.53Ga0.23Al0.24As/InP QD 1.55 μm TUNNEL INJECTION LASER 9

Fig. 2. (a) Schematic of the tunnel injection quantum dot laser heterostruc-ture; (b) calculated mode profile.

III. RESULTS AND DISCUSSION

A. Static Characteristics

The modal gain of the QD laser near threshold condi-tions was measured by the Hakki-Paoli technique [33]. Thesubthreshold spectra were measured with an optical spectralanalyzer under 10 kHz pulsed bias with duty cycle of 1.96%at room temperature. When threshold is reached, the spectraloutput is characterized by a succession of peaks and valleys.The spectral gain is determined by analyzing these data. Thenet modal gain �g, where g is the material gain, is plottedin Fig. 3(b) as a function of photon energy for a 50 μm ×1000 μm broad area laser. The measured peak modal gain is72.5 cm−1, and the modal gain per dot layer is 14.5 cm−1.This is comparable to the highest gain measured in any GaAs-or InP-based quantum dot laser and suggests that we have usedthe optimum number of QD layers [30] in the active region.

The light-current (L-I) characteristics of a broad area laserwas measured with pulsed bias (1.96% duty cycle) and isshown in Fig. 4(a). A small threshold current density of Jth =390 A/cm2 is obtained with as-cleaved facets. The thresholdcurrent Ith for this device is 195 mA. Even lower valuesare achievable by coating the facets with dielectric Braggreflectors. The spectral output of the laser for an injectioncurrent of 255 mA is shown in the inset to Fig. 4(a) withthe peak emission wavelength at 1.56 μm. The output light-current-voltage (L-I-V) characteristics of a 3 μm × 390 μmridge waveguide device are shown in Fig. 4(b).

Temperature dependent measurements were made on thelasers in the range of 0-75 °C. The variation of threshold

Fig. 3. (a) Room temperature photoluminescence (PL) spectrum ofInAs/In0.53Ga0.23Al0.24As/InP quantum dots; (b) gain spectrum of the quan-tum dot laser measured from the near-threshold laser spectrum (shown in theinset) using the Hakki-Paoli technique.

current density with temperature for a 1000 μm long broadarea laser is shown in Fig. 4(c). Analyzing the data withthe relation yields values of the temperature coefficient ofTo = 227 K in the range 5° ≤ T ≤ 45 °C and To =100 K in the range of 45° ≤ T ≤ 75 °C. These are largevalues of To in the context of 1.55 μm lasers [29], [30].We attribute this improvement to the tunnel injection of thecold electrons into the dots and their radiative recombinationbefore they can contribute to Auger recombination and leakageinto the barrier regions. The higher conduction band offsetin the In(AlGa)As material system is also responsible forthe observed improvement. The variation of peak emissionwavelength with temperature for lasers with different cavitylengths is shown in Fig. 4(d). The temperature and wavelengthrange represent the practical operational regimes for theselasers. The temperature coefficient dλ/dT shows a very smallchange, from 0.39 nm/K to 0.45 nm/K, in going from 0.5 mmto 2 mm in cavity length. The behavior does not indicateany significant gain saturation or state filling of the groundstate [34], as expected from the measured high value of modalgain, and instead reflects the normal bandgap shrinkage withtemperature.

We next describe measurements made on lasers with varyinglengths, L. The variation of peak emission wavelength isshown in Fig. 5(a). As mirror losses increase with decreasingcavity length, the required additional gain can be obtainedfrom transitions involving higher energy levels within the

10 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 50, NO. 1, JANUARY 2014

Fig. 4. (a) Measured light-current characteristics of a broad area quantum dot laser. Inset shows the lasing spectrum at I = 1.3Ith; (b) L-I-V characteristics ofa 3 μm × 390 μm ridge-waveguide laser showing the roll-over at high injection; (c) threshold current density vs. temperature characteristics of the broad-areaquantum dot laser of (a); (d) variation of peak wavelength with temperature for broad area lasers of varying cavity lengths.

ground state. It may be remembered that the ground state levelsare inhomogenously broadened by coupling between dots ofvarying size and a two-fold spin degeneracy. Nonetheless, themeasured shift of 10.5 nm for a four-fold increase in L isvery small, in agreement with the temperature dependent data.Light-current measurements were made on lasers of varyingcavity length and the differential quantum efficiency, ηd, andJth were recorded for each length. Figure 5(b) shows thevariation of η−1

d with L. Assuming mirror reflectivities of0.30 and an unity injection efficiency, the data yield valuesof internal quantum efficiency ηi = 65.3 % and cavity lossαi = 7.8 cm−1. The latter, which includes scattering andabsorption losses at the facets, is reasonably low. Figure 5(c)shows a plot of Jth versus 1/L. Analysis of this data yieldsvalues of the transparency current density Jtr = 272 A/cm2

and differential gain dg/dn = 7.7 × 10−16cm2. In performingthis analysis, values of confinement factor � = 0.03, quantumdot fill factor ξ = 0.51, radiative lifetime τr = 1 ns [35] andthe value quoted above for αi were used.

B. Dynamic Characteristics

The small-signal modulation characteristics of 390 μm-longridge waveguide lasers (3 μm ridge width) were measuredunder pulsed bias conditions with a sweep oscillator, low-noise amplifier, high-speed detector and a spectrum analyzer.The measured response was calibrated for the losses due to

cables, connectors, bias network and dc blocking capacitor.The modulation response is shown in Fig. 6. A −3dB modula-tion bandwidth of 14.4 GHz was measured for an injection cur-rent of 67 mA, and the resonance frequency fr at this injectionlevel is 11.2 GHz. The response at different injection currentsis analyzed by the classical laser modulation response [8]:

|M( f )|2 ∞ 1

( f 2 − f 2r )2 + ( γd

2π )2 f 2(1)

where γd is the damping factor. The limitation to the mod-ulation response due to the quantum capture time τc, whichis related to carrier relaxation in the QD, is neglected and itis assumed that differential gain and gain compression limitthe modulation bandwidth. Since we tunnel electrons directlyinto the QD, this assumption is justified. Under theseconditions, the damping factor is related to the resonancefrequency by the approximate relationship γd ∼= K f 2

r . Theproportionality constant is the K-factor, which is a measure ofthe damping limited bandwidth. Analysis of the small-signalmodulation data of Fig. 6 using Eqn (1) yields the values ofγd and fr and the plot of γd versus f2

r is shown in Fig. 7(a).From the slope of this plot, a value of K = 0.40 ns isobtained. The maximum intrinsic modulation bandwidth isgiven by f−3d B(max) = 23/2π/K = 22.3 GHz for thesequantum dot lasers. Neglecting carrier transport effects, theK-factor is related to differential gain, gain compression

BHOWMICK et al.: HIGH PERFORMANCE InAs/In0.53Ga0.23Al0.24As/InP QD 1.55 μm TUNNEL INJECTION LASER 11

Fig. 5. (a) Measured variation of peak wavelength of broad area lasers with different cavity lengths; (b) variation of inverse differential slope efficiency withcavity length; (c) variation of threshold current with inverse cavity length.

factor ε and photon lifetime τp through the equation [8]:

K ∼= 4π2(ε

vgdgdn

+ τp) (2)

where vg is the photon group velocity and τp is the photonlifetime. The differential gain can also be derived from thesmall-signal modulation data using the relation [8]:

fr = 1

2π

[vg�(I − Ith) dg

dn ηi

Lwdact q

]1/2

(3)

where w is the cavity width and dact is the thickness of theactive region. The measured values of fr is plotted in Fig. 7(b)against (I-Ith)

1/2 and a value of dg/dn = 8.1 × 10−16cm2 isderived from the slope of this plot. This value of differentialgain is in excellent agreement with that derived from thecavity length dependent L-I characteristics (Fig. 5(c)). Theseare amongst the highest values of differential gain measuredin 1.55 μm quantum well and quantum dot lasers [21]. Thevalue of the gain compression factor is then obtained by theuse of Eqn (2) as ε = 5.42 × 10−17 cm3. The low value ofε is a direct consequence of p-doping and tunnel injection ofelectrons, which minimizes the density of hot carriers due tohigher density of states in the QD wetting layer and barrierstates than that in the dots.

One of the consequences of the generation of hot carriersand gain compression in a laser under small-signal modulationis frequency, or wavelength, chirping caused by changes in therefractive index in the gain region. It is therefore of interest

Fig. 6. Measured small signal modulation response of ridge waveguidetunnel injection quantum dot laser. The solid curves are calculated modulationresponses (see text) The −3db modulation bandwidth measured for I = 67 mAis 14.4 GHz.

to measure this characteristic of the tunnel injection lasersunder study. We have measured chirp in the QD lasers duringsmall-signal modulation by measuring the broadening of asingle longitudinal mode using an optical spectrum analyzer.The sinusoidal modulation current was superimposed on thepulsed dc bias current above threshold. The envelope ofthe dynamic shift in the wavelength was recorded and thedifference between the half-width of the observed envelopewith and without modulation was used to evaluate the chirp.The measurements were done as a function of the frequency

12 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 50, NO. 1, JANUARY 2014

Fig. 7. Data obtained from analysis of small-signal modulation resonanceof QD lasers: (a) variation of damping factor with resonance frequency;(b) variation of resonance frequency with current injection.

of the modulating current. Shown in Fig. 8(a) is the measuredchirp as a function of the modulation frequency for a peak-to-peak modulation current of 5.5 mA. Dense and ultra-densewavelength division multiplexing schemes require narrowemission linewidth with a low dynamic chirp of the emissionwavelength [36]. The conventional light source at 1.55 μm hasbeen the InGaAsP double heterostructure or multi-quantumwell (MQW) laser which has large values of chirp (≥ 2 Ao)[37], [38]. In comparison, the measured chirp in the presentdevice is less than 1 Ao. An important related parameter is thelinewidth enhancement factor, or α-parameter, which is alsorelated to the effects of the change of refractive index withvariation of injection current on the dynamic characteristics ofthe laser. The α-parameter is expressed as: α = − 4π

λ

(dnr /dndg/dn

)and is determined by Hakki- Paoli measurements using therelation:

α = 2

δλ

dλ j

d{ln

[(√r j − 1

)/(√

r j + 1)]} (4)

where λj is the peak wavelength of the jth mode in thenear-threshold spectrum, rj is the peak-to-valley ratio in thespectrum and δλ is the mode spacing between adjacent modes.The measured α-parameters are plotted against the peak wave-length of the spectrum at threshold in Fig. 8(b) and theyexhibit a strong wavelength dependence. At and near the peakemission wavelength of 1.56 μm, α ∼0 and increases to above1.5 at both shorter and longer wavelengths. It has been shown

Fig. 8. Measured chirp of quantum dot laser as a function of small-signalmodulation frequency; (b) measured α-parameter as a function of emissionwavelength.

theoretically that the wavelength for the minimum value of αcoincides approximately with that of the peak gain in quantumdot and quantum wire lasers [39]. A similar trend has alsobeen observed in multi-quantum well and quantum dash lasers[40], [41]. Overall, the extremely low values of chirp andα-factor measured in these p-doped tunnel injection 1.55 μmlasers are very favorable characteristics.

Finally, it is worth noting that while improvement in laserperformance has been demonstrated in the present study withthe incorporation of p-doping of the dots and tunnel injectionof electrons, further improvement of laser characteristics havebeen proposed with tunnel injection of both electrons andholes. The double tunneling injection scheme [42], [43] helpsto prevent leakage of injected electrons and holes from theactive QD and can therefore lead to higher To and higheroutput powers.

IV. SUMMARY

The growth and application of self-organized InAs quantumdots on InP-based semiconductors is relatively new— thenanostructures that are formed more easily by self-organizationare quantum dashes. However, the characteristics of quantumdash lasers are not suitable for application in optical com-munication networks due to very high threshold currents andsmall To. We have therefore made a detailed investigationof self-organized InAs/ In0.53Ga0.23Al0.24As/InP quantum dotsand QD lasers grown by molecular beam epitaxy. The quantum

BHOWMICK et al.: HIGH PERFORMANCE InAs/In0.53Ga0.23Al0.24As/InP QD 1.55 μm TUNNEL INJECTION LASER 13

dots are fairly homogenous in size and have a large aerialdensity and quantum efficiency. Tunnel injection and p-dopingwere incorporated in the design of the laser heterostructureto minimize hot-carrier effects. The lasers are characterizedby relatively low threshold, very high To, large modulationbandwidth, small chirp and gain compression factor, and near-zero α-parameter. Most of these characteristics result fromlarge gain in the dot layers and large differential gain. Thedevices are therefore very attractive for application in long-haul optical communication networks.

REFERENCES

[1] U. Koren, B. I. Miller, Y. K. Su, T. L. Koch, and J. E. Bowers, “Lowinternal loss separate confinement heterostructure InGaAs/InGaAsPquantum well laser,” Appl. Phys. Lett., vol. 51, no. 21, pp. 1744–1746,1987.

[2] P. J. A. Thijs, L. F. Tiemeijer, P. I. Kuindersma, J. J. M. Binsma,and T. Van Dongen, “High-performance 1.5 μm wavelength InGaAs-InGaAsP strained quantum well lasers and amplifiers,” IEEE J. QuantumElectron., vol. 27, no. 6, pp. 1426–1439, Jun. 1991.

[3] B. I. Miller, U. Koren, M. G. Young, and M. D. Chien, “Strain-compensated strained-layer superlattices for 1.5 μm wavelength lasers,”Appl. Phys. Lett., vol. 58, no. 18, pp. 1952–1954, 1991.

[4] S. J. Caracci, M. R. Krames, N. Holonyak, M. J. Ludowise, andA. Fischer-Colbrie, “Long wavelength (λ ∼ 1.5 μm) native oxide de-fined InAlAs-InP-InGaAsP quantum well heterostructure laser diodes,”J. Appl. Phys., vol. 75, no. 5, pp. 2706–2708, 1994.

[5] X. Zhu, D. T. Cassidy, M. J. Hamp, D. A. Thompson, B. J. Robinson,Q. C. Zhao, et al., “1.4 μm InGaAsP-InP strained multiple-quantum-well laser for broad-wavelength tunability,” IEEE Photon. Technol. Lett.,vol. 9, no. 9, pp. 1202–1204, Sep. 1997.

[6] D. I. Babic, K. Streubel, R. P. Mirin, N. M. Margalit, J. E. Bowers,E. L. Hu, et al., “Room-temperature continuous-wave operation of1.54 μm vertical-cavity lasers,” IEEE Photon. Technol. Lett., vol. 7,no. 11, pp. 1225–1227, Nov. 1995.

[7] P. Bhattacharya, J. Singh, H. Yoon, X. Zhang, A. Gutierrez-Aitken, andY. Lam, “Tunneling injection lasers: A new class of lasers with reducedhot carrier effects,” J. Quantum Electron., vol. 32, no. 9, pp. 1620–1629,1996.

[8] D. Klotzkin, K.-C. Syao, P. Bhattacharya, C. Caneau, and R. Bhat,“Modulation characteristics of high speed (f-3dB = 20 GHz) tunnelinginjection InP/InGaAsP 1.55 μm ridge waveguide lasers extracted fromoptical and electrical measurements,” J. Lightw. Technol., vol. 15, no. 11,pp. 2141–2146, 1997.

[9] V. M. Ustinov, N. A. Maleev, A. E. Zhukov, A. R. Kovsh, A. Y. Egorov,A. V. Lunev, et al., “InAs/InGaAs quantum dot structures on GaAssubstrates emitting at 1.3 μm,” Appl. Phys. Lett., vol. 74, no. 19,pp. 2815–2817, 1999.

[10] O. B. Shchekin and D. G. Deppe, “Low-threshold high-T0 1.3 μmInAs quantum-dot lasers due to p-type modulation doping of the activeregion,” IEEE Photon. Technol. Lett., vol. 14, no. 9, pp. 1231–1233,Sep. 2002.

[11] P. K. Kondratko, S. L. Chuang, G. Walter, T. Chung, and N. Holonyak,“Observations of near-zero linewidth enhancement factor in a quantum-well coupled quantum-dot laser,” Appl. Phys. Lett., vol. 83, no. 23,pp. 4818–4820, 2003.

[12] S. Fathpour, Z. Mi, P. Bhattacharya, A. R. Kovsh, S. S. Mikhrin,I. L. Krestnikov, et al., “The role of Auger recombination in thetemperature-dependent output characteristics (T0 = ∞) of p-doped1.3 μm quantum dot lasers,” Appl. Phys. Lett., vol. 85, no. 22,pp. 5164–5166, 2004.

[13] S. Fathpour, Z. Mi, and P. Bhattacharya, “High-speed quantum dotlasers,” J. Phys. D, Appl. Phys., vol. 38, no. 13, pp. 2103–2111, 2005.

[14] Z. Mi, P. Bhattacharya, and S. Fathpour, “High-speed 1.3 μm tun-nel injection quantum-dot lasers,” Appl. Phys. Lett., vol. 86, no. 15,pp. 153109-1–153109-3, 2005.

[15] Y. Tanaka, K. Takada, M. Ishida, Y. Nakata, T. Yamamoto, M. Yam-aguchi, et al., “High-speed modulation in 1.3 μm InAs/GaAs high-density quantum dot lasers,” in Proc. Asia Commun. Photon. Conf.Exhibit., Dec. 2010, pp. 577–578.

[16] L. Gonzalez, J. M. Garcia, R. Garcia, F. Briones, J. Martinez-Pastor,and C. Ballesteros, “Influence of buffer-layer surface morphology onthe self-organized growth of InAs on InP(001) nanostructures,” Appl.Phys. Lett., vol. 76, no. 9, pp. 1104–1106, 2000.

[17] R. H. Wang, A. Stintz, P. M. Varangis, T. C. Newell, H. Li, K. J. Malloy,et al., “Room-temperature operation of InAs quantum-dash lasers onInP [001],” IEEE Photon. Technol. Lett., vol. 13, no. 8, pp. 767–769,Aug. 2001.

[18] H. Dery and G. Eisenstein, “Self-consistent rate equations of self-assembly quantum wire lasers,” IEEE J. Quantum Electron., vol. 40,no. 10, pp. 1398–1409, Oct. 2004.

[19] M. Gioannini, “Investigation of p-type doping effect on the gain charac-teristics of quantum dash semiconductor lasers,” Proc. SPIE, vol. 5452,pp. 526–533, Sep. 2004.

[20] P. Caroff, C. Paranthoen, C. Platz, O. Dehaese, H. Folliot, N. Bertru,et al., “High-gain and low-threshold InAs quantum-dot lasers onInP,” Appl. Phys. Lett., vol. 87, no. 24, pp. 243107-1–243107-3,2005.

[21] J. P. Reithmaier, A. Somers, S. Deubert, R. Schwertberger, W. Kaiser,A. Forchel, et al., “InP based lasers and optical amplifiers with wire-/dot-like active regions,” J. Phys. D, Appl. Phys., vol. 38, no. 13,pp. 2088–2102, 2005.

[22] D. Hadass, V. Mikhelashvili, G. Eisenstein, A. Somers, S. Deubert,W. Kaiser, et al., “Time-resolved chirp in an InAs/InP quantum-dashoptical amplifier operating with 10 Gbit/s data,” Appl. Phys. Lett.,vol. 87, no. 2, pp. 021104-1–021104-3, 2005.

[23] J. H. Wei and K. S. Chan, “A theoretical analysis of quantum dashstructures,” J. Appl. Phys., vol. 97, no. 12, pp. 123524-1–123524-12,2005.

[24] I. P. Marko, S. J. Sweeney, A. R. Adams, S. R. Jin, B. N. Murdin,R. Schwertberger, et al., “Recombination mechanisms in InAs/InPquantum dash lasers studied using high hydrostatic pressure,”Phys. Status Solidi B, vol. 241, no. 14, pp. 3427–3431,2004.

[25] F. Lelarge, B. Rousseau, B. Dagens, F. Poingt, F. Pommereau, andA. Accard, “Room temperature continuous-wave operation of buriedridge stripe lasers using InAs-InP (100) quantum dots as activecore,” IEEE Photon. Technol. Lett., vol. 17, no. 7, pp. 1369–1371,Jul. 2005.

[26] Z. Mi and P. Bhattacharya, “DC and dynamic characteristics of p-dopedand tunnel injection 1.65 μm InAs quantum-dash lasers grown on InP(001),” IEEE J. Quantum Electron., vol. 42, no. 12, pp. 1224–1232,Nov. 2006.

[27] C. Gilfert, E.-M. Pavelescu, and J. P. Reithmaier, “Influence of theAs2/As4 growth modes on the formation of quantum dot like InAsislands grown on InAlGaAs/InP (100),” Appl. Phys. Lett., vol. 96, no. 19,pp. 191903-1–191903-3, May 2010.

[28] S. G. Li, Q. Gong, Y. F. Lao, Y. G. Zhang, S. L. Feng, and H. L. Wang,“InAs/InP(100) quantum dot laser with high wavelength stability,”Electron. Lett., vol. 46, no. 2, pp. 158–159, 2010.

[29] D. K. Oh, J. S. Kim, J. H. Lee, S. U. Hong, C. W. Lee, W. S. Han,et al., “The progress of QD laser in the near IR wavelength region,”Proc. SPIE, vol. 7945, pp. 79450D-1–79450D-7, Jan. 2011.

[30] C. Gilfert, V. Ivanov, N. Oehl, M. Yacob, and J. P. Reithmaier, “Highgain 1.55 μm diode lasers based on InAs quantum dot like activeregions,” Appl. Phys. Lett., vol. 98, no. 20, pp. 201102-1–201102-3,2011.

[31] X. Zhang, A. Gutierrez-Aitken, D. Klotzkin, P. Bhattacharya, C. Caneau,and R. Bhat, “ 0.98-μm multiple-quantum-well tunneling injection laserwith 98-GHz intrinsic modulation bandwidth,” IEEE J. Sel. TopicsQuantum Electron., vol. 3, no. 2, pp. 309–314, Apr. 1997.

[32] Z. Y. Zhang, A. E. H. Oehler, B. Resan, S. Kurmulis, K. J. Zhou,Q. Wang, et al., “1.55 μm InAs/GaAs quantum dots and high repetitionrate quantum dot SESAM mode-locked laser,” Sci Rep., vol. 2, p. 477,Jun. 2012.

[33] B. W. Hakki and T. L. Paoli, “Gain spectra in GaAs double-heterostructure injection lasers,” J. Appl. Phys., vol. 46, pp. 1299–1306,Mar. 1975.

[34] V. Sichkovskyi, V. Ivanov, and J. P. Reithmaier, “High modal gain1.5 μm InP based quantum dot lasers: Dependence of static properties onthe active layer design,” Proc. SPIE, vol. 8640, pp. 864004-1–864004-6,Mar. 2013.

[35] N. A. Jahan, C. Hermannstädter, J. H. Huh, H. Sasakura, and T. J. Rotter,“Temperature dependent carrier dynamics in telecommunication bandInAs quantum dots and dashes grown on InP substrates,” J. Appl. Phys.,vol. 113, no. 3, pp. 033506-1–033506-11, 2013.

14 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 50, NO. 1, JANUARY 2014

[36] ITU-T G.694.1, International Telecommunication Union, Geneva,Switzerland, 2002.

[37] P. J. A. Thijs, L. F. Tiemeijer, P. I. Kuindersma, J. J. M. Binsma,and T. van Dongen, “High-performance 1.5 μm wavelength InGaAs-InGaAsP strained quantum well lasers and amplifiers,” IEEE J. QuantumElectron., vol. 27, no. 6, pp. 1426–1439, Jun. 1991.

[38] Y. Suematsu and S. Arai, “Single-mode semiconductor lasers for long-wavelength optical fiber communications and dynamics of semicon-ductor lasers,” IEEE J. Sel. Topics Quantum Electron., vol. 6, no. 6,pp. 1436–1449, Nov./Dec. 2000.

[39] T. C. Newell, D. J. Bossert, A. Stintz, B. Fuchs, K. J. Malloy,and L. F. Lester, “Gain and linewidth enhancement factor in InAsquantum-dot laser diodes,” IEEE Photon. Technol. Lett., vol. 11, no. 12,pp. 1527–1529, Dec. 1999.

[40] Y. Miyake and M. Asada, “Spectral characteristics of linewidth en-hancement factor α of multidimensional quantum wells,” J. Appl. Phys.,vol. 28, pp. 1280–1281, May 1989.

[41] P. J. A. Thijs, T. Dongen, L. F. Tiemeijer, and J. J. M. Binsma, “High-performance λ = 1.3 μm InGaAsP-InP strained-layer quantum welllasers,” J. Lightw. Technol., vol. 12, no. 1, pp. 28–37, Jan. 1994.

[42] L. V. Asryan and S. Luryi, “Tunneling-injection quantum-dot laser:Ultrahigh temperature stability,” IEEE J. Quantum Electron., vol. 37,no. 7, pp. 905–910, Jul. 2001.

[43] D.-S. Han and L. V. Asryan, “Output power of a double tunneling-injection quantum dot laser,” Nanotechnology, vol. 21, no. 1, pp. 015201-1–015201-14, Jan. 2010.

Sishir Bhowmick received the B.Sc. and M.Sc.degrees in electrical and electronic engineering fromthe Bangladesh University of Engineering and Tech-nology, Dhaka, India, in 2006 and 2008, respectively.He is currently pursuing the Ph.D. degree with theDepartment of Electrical Engineering and ComputerScience, University of Michigan, Ann Arbor, MI,USA. His research interests include growth and char-acterization of III–V based optoelectronic devices.He is currently working on high-speed quantum dotlasers, rolled-up microtube lasers, and quantum dot

terahertz detectors.

Md Zunaid Baten (S’09) received the B.Sc. andM.Sc. degrees in electrical and electronic engineer-ing from the Bangladesh University of Engineeringand Technology, Dhaka, India, in 2009 and 2012, re-spectively. He is currently pursuing the Ph.D. degreewith the Department of Electrical Engineering andComputer Science, University of Michigan, Ann Ar-bor, MI, USA. His research interests include growthand characterization of III–V and III-nitride basedoptoelectronic devices. He is currently working onhigh-speed quantum dot lasers and polariton lasers.

Thomas Frost (S’08) is currently pursuing theDoctoral degree with the Department of ElectricalEngineering and Computer Science, University ofMichigan, Ann Arbor, under the supervision of Prof.P. Bhattacharya. He received the B.S. degree in en-gineering from the University of Michigan in 2011.His research interests include growth and characteri-zation of III-nitride based optoelectronic devices. Heis currently working on molecular beam epitaxialgrowth and optimization of InGaN/GaN quantumdots and the characterization of ridge geometry

lasers incorporating quantum dots in the active region.

Boon S. Ooi (M’95–SM’03) received the Ph.D.degree in electronics and electrical engineering fromthe University of Glasgow, U.K. He served as a Fac-ulty Member with Nanyang Technological Univer-sity, Singapore, and Lehigh University, USA, beforejoining the King Abdullah University of Science andTechnology as a Professor of electrical engineeringin 2009. His research interests include semiconduc-tor lasers and photonics integrated circuits. He is afellow of the SPIE and the Institute of Physics, U.K.

Pallab Bhattacharya (M’78–SM’83–F’89) is theCharles M. Vest Distinguished University Professorof electrical engineering and computer science andthe James R. Mellor Professor of engineering withthe Department of Electrical Engineering and Com-puter Science, University of Michigan, Ann Arbor.He received the M.Eng. and Ph.D. degrees from theUniversity of Sheffield, U.K., in 1976 and 1978,respectively. He was an Editor of the IEEE TRANS-ACTIONS ON ELECTRON DEVICES and Editor-in-Chief of the Journal of Physics D. He has edited

Properties of Lattice-Matched and Strained InGaAs (INSPEC, 1993) andProperties of III–V Quantum Wells and Superlattices (INSPEC, 1996). Hehas authored the textbook Semiconductor Optoelectronic Devices (PrenticeHall). His teaching and research interests are in the areas of compoundsemiconductors, low-dimensional quantum confined systems, nanophotonics,spintronics, and optoelectronic integrated circuits. He is currently workingon high-speed quantum dot lasers, nitride-based visible quantum dot lasersand LEDs, nanowire heterostructures, cavity quantum electrodynamics, andpolariton lasers.

He is a member of the National Academy of Engineering. He receivedthe John Simon Guggenheim Fellowship, the Heinrich Welker Medal, theIEEE Paul Rappaport Award, the IEEE Engineering Achievement Award, theIEEE Nanotechnology Pioneer Award, the Optical Society of America NickHolonyak Award, the TMS John Bardeen Award, the SPIE Technical Achieve-ment Award, and the Quantum Devices Award of the International Symposiumon Compound Semiconductors. He received the S.S. Attwood Award, theKennedy Family Research Excellence Award, and the Distinguished FacultyAchievement Award from the University of Michigan. He is a fellow of theAmerican Physical Society, the Institute of Physics, and the Optical Societyof America.