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IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 39, NO. I I . NOVEMBER 1992 265 1

tivity. The effect of external field on gas adsorption in- dicates that O2 adsorption is almost completely suppressed at the external bias of + 18 V for the investigated range of O2 pressure for both Pd-SnO, and Pd-ZnO devices. This property eliminates necessity of keeping the device under vacuum or encapsulated before the application. However, device with Pt as catalyst showed no electro- induced gas adsorption effect. This might be due to the difference in catalyst sensitization mechanism involved.

This work was supported by Research Initiation Award through the NSF.

IIIB-1 Electrically Pumped, Room-Temperature Mi- crodisk Semiconductor Lasers with Submilliampere Threshold Currents-A. F. J. Levi, R. E. Slusher, S. L. McCall, T. Tanbun-Ek, D. L. Coblentz, and S. J. Pearton, AT&T Bell Laboratories, Murray Hill, NJ 07974.

We demonstrate electrically pumped whispering-gal- lery mode microdisk lasers with single-mode operation and submillampere threshold current at room tempera- ture. Semiconductor microdisks !O pm in diameter and 340 nm thick including foyr 100- A InGaAs quantum well layers separated by 150-A InGaAsP barriers are fabri- cated with InP support pedestals above (p-type) and be- low (n-type) the disk. A 4.5-pm-diameter metal disk atop the p-type pedestal provides electrical contact to the laser structure. The semiconductor disks form high-Q optical resonators for the whispering-gallery mode around the edge of the disk [ l ] . Electrical pulses 0.3 ps in length at levels near 1 V and 1 mA result in lasing at room tem- perature for wavelengths near 1.58 pm with emission from the edge of the disk. At 1-mA current levels the peak laser emission is 9 dB above the spontaneous emission back- ground and at 8 mA it is 26 dB above the background. Single-mode operation is obtained at the lower range of pump current. Heating effects are observed at the higher pump currents. These low-threshold microlasers have po- tential for high-density microphotonic circuits. Coupling into waveguide structures, circuit possibilities and speed performance will be discussed. 111 S. L. McCall, A. F. J . Levi, R. E. Slusher, S . J . Pearton, and R . A.

Logan, Appl. Phys. Lerr., vol. 60, p. 289, 1992.

IIIB-2 Fabrication of Low-Threshold Voltage Micro- lasers-A. Scherer, J. L. Jewell,* M. Walther, J . P. Har- bison, and L. T. Florez, Bellcore, 331 Newman Springs Rd., Red Bank, New Jersey 07701 (908) 758-3367.

We have reduced the voltage required for threshold in vertical cavity surface emitting lasers (VCSEL’s) to 1.7 V. Molecular beam epitaxy (MBE) was used to grow 30 pairs of n-doped Alo. 15GaAs /AlAs bottom mirrors and the active p-n junction with a 1-pm p-doped top contact. 12 pairs of alternating Si02/Si3N, layers formed a high-re-

flectivity mirror which was used to complete the laser cavity. We have evaluated these reactive sputter-depos- ited mirrors by using finesse measurements in resonator structures, and obtain reflectivities of above 98% in 9.5 pairs. Individual laser elements were defined by ion etch- ing through the p-n junction, followed by planarization with Si02 to define the current path. Then, Au-Zn p-contacts were deposited and alloyed for lateral current injection. Finally, another ion milling step was used to isolate individual contacts. Lasers with widths ranging from 7.5 to 25 pm were fabricated and measured.

In these lasers, 850-nm light is generated by three IO-nm GaAs quantum wells and is emitted through an an- nular p contact. The p resistance is reduced by heavily beryllium-doping the top of the cavity. This configuration reduces the series resistance to below 70 Q for 12-pm laser elements. The threshold currents and voltages of 12-pm diameter lasers were measured to be 3 mA and 1.7 V, respectively. We also determined peak output powers of from 12-pm devices, and obtain 1 mW when lasers are pulsed at 1 % duty cycle with 20 mA. We can also operate these lasers by CW pumping. However, the threshold cur- rent increases to approximately 5 mA. We also find that the emission wavelength of our lasers can be deliberately shifted (from 850 to 855 nm) by altering the thickness of the dielectric output mirrors.

We show that the combination of high-reflectivity di- electric mirror layers with accurate MBE growth can be used to significantly reduce the power requirements of in- dividual laser elements. We expect that this advance will allow us to integrate large numbers of VCSEL devices into complex arrays without the heat-dissipation problems found in more conventional VCSEL designs [ 13. Finally, the relatively shallow depth of the active area from the semiconductor surface allows us to greatly simplify the VCSEL fabrication process.

Broomfield, CO 8002 1

[ 11 J . L. Jewell, J . P. Harbison, A. Scherer, Y. H. Lee, and L. T. Florez, “Vertical cavity surface emitting lasers: Design, growth, fabrication, characterization,” IEEE J . Quantum Electron., vol. 27, p. 1332, 1991.

*J. L. Jewell is with Photonic Research Inc., 100 Technology Drive, (303) 465-649 1 .

IIIB-3 Room-Temperature Pulsed Operation of a 1.5-pm GaInAsP/InP Vertical Cavity Surface Emit- ting Laser-T. Tadokoro, H. Okamoto, Y. Kohama, T. Kawakami, and T. Kurokawa, NTT Opto-electronics Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan.

This paper reports on lasing characteristics of Ga- InAsP /InP vertical cavity surface emitting laser diode (VCSELD) whose oscillation wavelength is 1.58 pm. The threshold current density is around 21 kA/cm2, which is lower than previously reported results in long-wavelength GaInAsP/InP systems [ 13, [2].

The double heterostructure was grown by metal-or- ganic chemical vapor deposition (MOCVD) on a (100)