34 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO. 1, JANUARY 1997

An Integrated PIN/MISS OEIC for HighCurrent Photoreceiver Applications

Y. K. Fang, Kun-Hsien Lee, Kun-Hsien Wu, and Chung-Yang Tsao

Abstract— A new PIN/MISS photoreceiver with very highoutput current has been developed by using the combination of anamorphous silicon germanium alloy PIN photodiode and a metal-insulator-semiconductor switch (MISS) device. The developedphotoreceiver uses a PIN photodiode as the light absorptionstructure and light wavelength selector and the MISS device as anactuator to drive an electronic load. Based on the experimentalresults, the photoreceiver yields a very high output current of3.2 mA at a voltage bias of 6 V under an incident light powerof Pin = 100 �W, and has a rise time of 465�s with a loadresistance ofR = 1 k. The peak response wavelength of thePIN photodiode is at 905 nm, i.e., infrared light. Thus the highoutput current PIN/MISS photoreceiver is a good candidate forsome specific applications.

I. INTRODUCTION

USUALLY a photoreceiver is used for high sensitivityoptical fiber communication system or where a high

output current is needed to drive some electronic load circuit.In past, most of the receiver have been prepared based onIII–V compound material with a structure of PIN/FET orPIN/MODFET for the purpose of high sensitivity [1]. Fewreports have been found on the object of high output current. Inthis paper, we propose a new PIN/MISS OEIC for high outputcurrent photoreceiver applications. The developed receiver isbased on silicon material, thus possessing low cost and VLSIcompatible advantages. To meet the high current object, wetry the MISS (metal-insulator-semiconductor switch) structureinstead of FET or MODFET (modulation doped FET). TheMISS has been proved to be a high speed switching elementwith a high current driving ability [2]. In addition, usingthe MISS as current output can omit the followed amplifiersystem and driving the load, e.g., LED’s or relays directly, thusenhancing the whole system speed. In preparing MISS, a lowtemperature process for insulating layer has been considered toprotect the P/N junction under the insulating layer. Therefore,an amorphous silicon layer ( 250 C) [3]–[8] has beenemployed instead of conventional SiO(1000 C 1100 C)[9], Si N (700 C 900 C) [9] and polysilicon (500 C 900C) [9].

Futhermore, in preparing PIN detectors, the low temperatureprocess is considered again so that the under MISS’s original

Manuscript received October 25, 1995; revised July 16, 1996. The reviewof this paper was arranged by Editor P. K. Bhattacharya. This work wassupported by the Science Council of R.O.C. under Contract NSC 83-0417-E-006-001.

The authors are with the VLSI Technology Laboratory, Department ofElectrical Engineering, National Cheng Kung University, Tainan 70101,Taiwan, R.O.C.

Publisher Item Identifier S 0018-9383(97)00302-X.

Fig. 1. The schematic cross sections of the new high output currentPIN/MISS photoreceiver.

characteristics can be kept unchanged. To meet the purpose,we select the amorphous silicon and its alloy as materials (seeFig. 1). Especially, undoped amorphous silicon-germaniumalloy (i- -Si Ge :H) is employed as ligh absorption layerin the detector possessing another advantage of light wave-length selection ability. The peak response wavelength ofi- -Si Ge :H can be designed for UV (ultra-violet), redor IR (infra-red) just to change the composition ratioofthe layer. A detailed report of the selection ability of i-

-Si Ge :H material can be found elsewhere [7]. In thefollowing sections, the fabrication process, operation mecha-nism, spectral response, I–V curves and photoresponse speedare discussed in detail.

II. DEVICE STRUCTURE AND FABRICATION

Fig. 1 shows the schematic cross section of the new highoutput-current PIN/MISS photoreceiver. The fabrication pro-cesses are as follows: 1) A crystalline plate was usedas a substrate. 2) The 300A 2500 A undoped -Si:H layerwas deposited by using plasma-enhanced chemical vapordeposition (PECVD) system. 3) A 5000A Au layer wasdeposited by thermal evaporation and used as the anodecontact . 4) The area of the MISS device was definedwith photolithography. 5) A 5000A Au layer was depositedon the back side of the MISS device and used as the cathodecontact . 6) Then to deposite a 375A p-type -Si:Hlayer, a 6000 7500 A undoped -Si Ge :H layer, and a

0018–9383/97$10.00 1997 IEEE

FANG et al.: INTEGRATED PIN/MISS OEIC FOR HIGH CURRENT PHOTORECEIVER APPLICATIONS 35

(a)

(b)

Fig. 2. The energy band diagram of the MISS device under (a) the occur-rence of switching behavior and (b) the ON-state after switching.

Fig. 3. A typical I–V curve of the developed MISS device. The insertionshows its photograph with scale:I = 1 mA/div., V = 3 V/div.

500 A n-type -Si:H layer were deposited sequentially byusing a PECVD system. 7) Next, an 1000A Indium-TinOxide (ITO) layer was deposited by using a E-gun evaporationsystem. 8) Finally, the photolithography technology was usedto define the area of the PIN photodiode. The effective areasof the MISS device and PIN photodiode are 1 mmand 3.19mm , respectively. The RF power, substrate temperature andtotal pressure during deposition of-Si:H are 50 W, 250 C,and 1 Torr respectively; and the during deposition of the-Si Ge :H are 40 W, 250 C, and 0.5 Torr, respectively.The gases used are SiH(25% in H ) and SiH (25% inH ) GeH (47.8% in H ). The thickness of each layer was

estimated and controlled by growth rate, which is 60A/minfor -Si:H deposition and 200A/min for -Si Ge :H underthese conditions.

III. OPERATION MECHANISM OF

THE PIN/MISS PHOTORECEIVER

The energy band diagram of the MISS device under the oc-currence of switching behavior and the ON-state after switch-ing are shown in Fig. 2(a) and (b), respectively. For conve-nience, the diagram is idealized, thereby ignoring the effect ofsurface state, fixed charge, and work function difference. Asa positive voltage with respect to the cathode is applied to theanode, the majority of the applied voltage is dropped across thereverse biased MIS region and the rest of the applied voltage isdropped across the c-Si p-n junction, as shown in Fig. 2(a). Ifthe applied voltage increases positively, the depletion region inthe p-type c-Si layer under the anode grows. Simultaneously,electron-hole pairs are generated in this depletion region,creating a leakage current. Continuously increasing the appliedvoltage, extra electrons are thus injected from the n-type c-Si layer to i- -Si/p-c-Si interface. If the electron current istunnelling-limited, the accumulated electrons at the interfaceincrease with a concomitant increase of the voltage drop acrossthe undoped -Si:H semi-insulator. When the magnitude ofthe accumulated electrons is large enough, a build-up of theinversion charge takes place, as depicted in Fig. 2(b). Thusthe electric field in the semi-insulator increases, allowing alarger tunneling current to pass. The augmented current isforced back through the p-n junction, thus turning it furtheron. Therefore, a positive feedback process is established. TheMISS device display a negative resistance characteristic. Thevoltage across the device is collapsed, and the conductingcurrent is rapidly increased.

The detailed switching behavior of the MISS device withthe gate terminal connected to the p-type c-Si layer is decribedas follows. When a positive current is applied to the gateterminal, the switching voltage changes in according to thegate current. The injection of positive gate current decreasesthe barrier height of the p-n junction, thus increasing thecarrier injection. Therefore, avalanche multiplication occursat a lower applied voltage. decreases with increasing thepositive gate current. In this study, the gate contact is replacedby the amorphous silicon germanium alloy PIN photodiode.Therefore, the switch mechanism of the MISS device iscontrolled by the photocurrent of the PIN photodiode.

Fig. 3 shows a typical I–V curves of the developed MISSdevice.The inserted photograph shows its detailed scales. Asmentioned in above, in normal operation, the MISS is biasedwith a DC power supply between anode and cathod and thegate contact is used as the switch point (see Fig. 1). As shownin the figure, before the switch voltage , the MISS deviceis operated in a high voltage and low current state, i.e., OFFstate. If a trigger current is added on the gate contact, the MISSdevice will be turned into a low voltage and high current state,i.e., ON state, also the voltage will be hold on the specifiedhold voltage . As the MISS device is switched from a highvoltage state (i.e., ) into a low voltage state (i.e., ), the

36 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO. 1, JANUARY 1997

(a)

(b)

Fig. 4. The equivalent circuit of the PIN/MISS photoreceiver under (a)without (b) with infrared signal input.

high voltage difference between and will across on theload and contribute a high output current as can be seen fromFig. 4(a) and (b), where is the voltage to bias the PINdiode and is the external DC power supply for MISS.This is the reason why MISS device can provide a very highoutput current. As light illuminates on the PIN photodiode,the undoped -Si Ge :H layer will absorb the incident lightand generate the photocurrent. As the photocurrent is injectedinto the p-type c-Si layer, it will switch the state of the MISSdevice and generate a high output current from the voltagedifference between and .

IV. EXPERIMENTAL RESULTS AND DISCUSSIONS

As mentioned in above, the high output current is deter-mined by the voltage difference between and , hencethe factors controlling the voltage and are interestingand have been studied in detail. Fig. 5 shows the effect ofthe undoped -Si:H layer thickness on the switching voltage

and holding voltage . The and are increasedwith increasing the undoped-Si Ge :H layer thicknessdue to the longer tunneling distance of the undoped-Si Ge :H layer which will effect the tunnel probability.As Fig. 5 shows, the maximum voltage difference between

and is researched with a 1200A undoped -Si:H layerand a voltage difference of about 6 V. The leakage current

Fig. 5. The switching voltage(Vs) and the holding voltage(Vh) of theMISS device measured under different undoped�-Si:H layer thickness.

Fig. 6. The spectral responses of the PIN diode with 7500A undoped�-Si:Hlayer and the MISS device with 7500A undoped�-Si:H layer, respectively.

under this condition is about 100A, which will be toolarge for some applications. However, for some applicationswith high voltage operation and high output current, a thickerundoped -Si:H layer should be used to protect the devicefrom breakdown. In this study, to detect very low level ofincident light and to reduce the noise amplification from theleakage current, the thickness of the undoped-Si:H layer isset at 500A the leakage current and voltage difference between

and are 40 A and 3.2 V, respectively. Therefore, fora load resistance k , the output current of the MISSdevice will be 3.2 mA, which is large enough to drive theelectronic devices such as LED’s. Furthermore, with a smallerload resistance, e.g., , the output current can be aslarge as 400 mA. In addition, decreasing the thinner undoped

-Si:H layer thickness will decrease the series resistance ofthe MISS device, which will contribute to a higher switchingspeed.

In determining the diodes’ responsivity, a Bausch andLomb monochrometer with appropriate grating was used asthe light source. As mentioned above, the amorphous silicongermanium PIN photodiode is selected as light absorptionstructure and light wavelength selector, especially the undoped

-Si Ge :H layer was used for its variety of peak responsewavelength is achieved by changing the composition. Fig. 6shows the photoresponses of the PIN diode and the MISS

FANG et al.: INTEGRATED PIN/MISS OEIC FOR HIGH CURRENT PHOTORECEIVER APPLICATIONS 37

Fig. 7. Dark and photo I–V characteristics of the PIN photodiode at variousincident light power levels. The traces sequentially correspond to 100�W,65 �W, 50 �W, 30 �W, 20 �W, 0 �W.

device, respectively. In the figure, we find the PIN has aphotoresponse almost 20 times higher than that of the MISS.This is due to the design consideration for various functions.In this case, the MISS has been designed as an actuator andthe i- -Si Ge :H layer in the MISS structure is used asan insulating layer not as a light absorption layer. Hence anAu contact (500A), not ITO, was deposited on the top of i-

-Si Ge :H as an electron contact and this will contributeto low light absorption efficiency since the thick Au layer isnot transparent to the light. In addition, the MISS device isoperated under forward bias and the PIN is operation underreverse bias, which will enhance the absorption area and carrierseparation. Therefore, the responsivity of the PIN photodiodeis higher than the responsivity of the MISS. As experimentalresults show, with a 7500A undoped -Si Ge :H layerand an value of 0.48, the peak response wavelength of thePIN diode is at 905 nm, i.e., infrared light. In addition, Fig. 6shows that spectral response of the MISS device is almostwide-band response, i.e., no wavelength selectivity. Therefore,by combination with the PIN photodiode, the new PIN/MISSphotodetector has the features of light wavelength selectivityand high output current and these characteristics are importantfor some specific applications.

Fig. 7 shows the I–V curves of the PIN photodiode atdifferent incident light power. The incident light power isemitted from a laserdiode with wavelength nm andintensity of 5 mW. As the results show, with incident lightpower is 20 W and voltage reverse bias is at 6 V, thephotocurrent of the PIN diode is about 250A which is largeenough to trigger the switch of the MISS device from the OFFstate to the ON state. These experimental results show that theMISS device can be switched even by a low photocurrent froma conventional PIN photodiode. In other words, with very lowlevel of incident light power, the PIN/MISS photodetector stillcan detect the light, switch the OFF/ON state, and generate avery high output current to drive the load resistance.

Finally, the photoresponse speed of the PIN/MISS photode-tector was measured under the illumination of an infrared LED( nm) with an average power intensity of 100W andsquare wave of 200 Hz, as shown in Fig. 8. The photodetectorwas in series with a load resistance of k . The

Fig. 8. The photoresponse of the PIN/MISS photoreceiver under 6 V reversebias and illumination of infrared LED (� = 820 nm) with intensity of 100�W and square wave of 200 Hz. The photodetector was also in series witha load resistanceR = 1 k.

measured rise time and fall time of the photodetector with6 V reverse bias are 465s and 375 s, respectively. The lowresponse speed can be explained as follows: 1) The minoritycarrier recombination time is long in the ohmic contact region,and 2) the density of interface traps is high between the p-type

-Si:H layer and p-type c-Si layer. As the photo generatedcarriers flow from the PIN diode into the MISS structure,the carriers are captured by the traps are contribute to longerresponse time. 3) Also, the electron drift mobility of theundoped -Si Ge :H material is much lower than that ofthe undoped -Si:H material [10]. With increased value, thedrift mobility decreases even further. 4) The area of the PINdiode is large which will increase capacitance and then enlargethe RC time. Therefore, the response time of the PIN/MISSphotodetector is much longer than that of crystal silicon.

V. CONCLUSION

The structure, operation mechanism, spectral response, andother characteristics of the new PIN/MISS IR photoreceiverhave been reported in detail. The major features of thePIN/MISS photoreceiver are low-cost, low-noise performance,very high current driving ability, and VLSI compatibility.In addition, by changing the Ge atomic ratio of the

-Si Ge :H layer, the new PIN/MISS photodetector alsocan detect red light or UV light as desired. Based on thefeatures mentioned above, especially very high output currentand light wavelength selectivity, the developed new PIN/MISSphotoreceiver is a candidate for some specific applications.

REFERENCES

[1] P. Bhattacharya,Semiconductor Optoelectronic Devices. EnglewoodCliffs, NJ: Prentice-Hall, 1994, ch. 12.

[2] S. M. Sze, Physics of Semiconductor Devices, 2nd ed. New York:Wiley, 1981, ch. 9.

[3] J. W. Hong, W. L. Laih, Y. W. Chen, Y. K. Fang, C. Y. Chang, andJ. Gong, “Optical and noise characteristics of amorphous Si/SiC su-perlattice reach-through avalanche photodiodes,”IEEE Trans. ElectronDevices, vol. 37, pp. 1804–1809, Aug. 1990.

[4] S. C. Jwo, M. T. Wu, Y. K. Fang, Y. W. Chen, J. W. Hong, and C.Y. Chang, “Amorphous silicon/silicon carbide superlattice avalanchephotodiodes,”IEEE Trans. Electron Devices, vol. 35, pp. 1279–1283,Aug. 1988.

38 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO. 1, JANUARY 1997

[5] J. W. Hong, Y. W. Chen, W. L. Laih, Y. K. Fang, and C. Y. Chang, “Thehydrogenated amorphous silicon reach-through avalanche photodiodes(a-Si:H RAPD’s),” IEEE J. Quantum Electron., vol. 26, pp. 280–284,1990.

[6] K. H. Lee, Y. K. Fang, and G. Y. Lee, “A normal amorphous siliconbased separate absorption and multiplication avalanche photodiode(SAMAPD) with very high optical gain,”IEEE Trans. Electron Devices,vol. 42, p. 1929–1933, Nov. 1995.

[7] S. B. Hwang, Y. K. Fang, K. H. Chen, C. R. Liu, J. D. Hwang, andM. H. Chou, “An a-Si:H/a-SiGe:H bulk barrier phototransistor with�-SiC:H barrier enhancement layer for high gain IR optical detector,”IEEE Trans. Electron Devices, vol. 40, pp. 721–726, Apr. 1993.

[8] Y. K. Fang, C. R. Liu, K. H. Chen, and C. H. Lin, “A low cost andhigh current gain a-Si/c-Si heterojunction photoreceiver for large areaoptoelectronics integrated circuit applications,”IEEE Electron DeviceLett., vol. 16, pp. 190–192, May 1995.

[9] S. M. Sze,VLSI Technology, 2nd ed. New York: McGraw-Hill, 1988,ch. 6.

[10] J. Kanicki, Amorphous and Microcrystalline Semiconductor DevicesVolume II: Materials and Device Physics. Boston, MA: Artech House,1992.

Y. K. Fang was born in Taiwan, R.O.C., on October10, 1944. He received the B.S. and M.S. degrees inelectronics engineering from National Chiao TungUniversity, Hsinchu, Taiwan, in 1957 and 1959,respectively, and the Ph.D. degree in semiconductorengineering from the Institute of Electrical andComputer Engineering, National Cheng Kung Uni-versity, Tainan, Taiwan, in 1981.

From 1960 to 1978, he was a Senior Designerand Research Engineer in the private sector. From1978 to 1980, he was an Instructor, then became

and Associate Professor in 1981, and a Professor in 1986 in the Departmentof Electrical and Computer Enginnering, National Cheng Kung University.

Dr. Fang is a member of Phi Tau Phi.

Kun-Hsien Lee was born in Taiwan, R.O.C., onSeptember 16, 1969. He received the B.S. andM.S. degrees in electrical engineering from NationalCheng Kung University, Tainan, Taiwan, in 1991and 1993, respectively.

His current research interests are in high opticalgain a-Si:H/a-SiGe:H heterojunction photodetectors.

Kun-Hsien Wu was born in Taiwan, R.O.C., onJuly 3, 1962. He received the B.S. and M.S. de-grees in electrical engineering from National ChengKung University, Tainan, Taiwan, in 1985 and 1987,respectively. Since 1994, he has been pursuing thePh.D. degree at the Institute of Electrical Engineer-ing, National Cheng Kung University. His currentstudy is to develop the silicon-carbide/silicon het-rojunction devices for high temperature and highpower applications.

Mr. Wu is a member of Phi Tau Phi.

Chung-Yang Tsao was born in Taiwan, R.O.C.,on January 5, 1970. He received the B.S. andM.S. degrees in electrical engineering from NationalCheng Kung University, Tainan, Taiwan, in 1993and 1995, respectively.