IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 35, NO. 12, DECEMBER 1988 2435

is implemented consisting of gain and level-shifting buffer stages with an open-loop voltage gain of 5.5. The amplifier employs a novel symmetrical design where the dc offset is zero at the output. A total of 12 components are integrated monolithically .

A receiver sensitivity of -36.4 dBm is measured from the in- tegrated PIN-JFET amplifier for 200 Mbit/s NRZ optical signals (1.3-pm wavelength) at 1 X bit error rate. This is the best sensitivity to our knowledge reported from a PIN-FET device de- signed for 1.3-1.55 pm wavelenth at this bit rate. [ I ] S. Kim, K. Wang, G. Vella-Coleiro, J. Lutze, Y. Ota, and G. Guth,

“A low power high speed ion-implanted JFET for InP-based mono- lithic optoelectronic ICs,” IEEE Electron Device Lett., vol. EDL-8, p. 518, Nov. 1987.

IIB-5 Theoretical and Experimental Studies of Monolithically Integrated Pseudomorphic InGaAs/AlGaAs MODFET-APD Photoreceivers-Y. Zebda, R. Lipa, M. Tutt, D. Pavlidis, P. K. Bhattacharya, J. Pamulapati, and J . E. Oh, Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109-2122.

The objective of our work is to gain a good understanding of the performance characteristics of pseudomorphic InGaAs/GaAs MODFET’s monolithically integrated with a GaAs/AlGaAs su- perlattice APD for low-noise photoreceiver applications. Previous work in the area of integration has mostly been in the development of the technology [ I ] and little has been reported on theoretical or experimental studies of the materials and architecture related lim- itations to device performance. The best reported integrated FET performance is a dc g, = 170 mS/mm [2] in a I-pm transistor and noise figure of 1.3 dB with 8-dB associated gain at 10 GHz in a 0.5-pm gate MODFET [3].

We have made a detailed theoretical analysis of the frequency response and noise performance of the integrated device, taking account of the material characteristics of the pseudomorphic In- GaAs/AlGaAs heterostructures and GaAs/AlGaAs MQW APD. In contrast to the conventional approach of inserting an equilization circuit at the output, we have investigated the effects of adding an inductor between the output on the detector and the input of the transistor and the effects of a feedback resistance on the noise, speed and gain characteristics. It is seen, for example, that as the in- ductance increases from 0.08 to 0.6 nH, the 3-dB cutoff frequency increases from 15 to 28 GHz for 20 X 25 pm photodiode and a 1-pm gate MODFET. In the noise analysis, in addition to the ef- fects of gate leakage, avalanche multiplication, and resistive and thermal components, the effects of traps in the active and isolating layers of the integrated structure have been taken into account.

We have fabricated and measured the performance characteris- tics of a monolithic device consisting of a InGaAs/AlGaAs pseu- domorphic single quantum well MODFET with 1-pm gate length apd a 30 X 50 pm APD with a 13-period GaAs/AlGaAs (400/400 A ) avalanching region on top of it and isolated from the FET by an AlGaAs layer. The devices were coupled with monolithic resis- tors and inductors and with air-bridge technology. The entire struc- ture was grown on GaAs substrates by MBE and we believe this is the first demonstration of a pseudomorphic and MQW integrated device. The highest measured g, of the integrated MODFET is 250 mS/mm over a 2-in wafer and this value is the best reported to date. The dc FET characteristics are also characterized by I,,, = 150 mA/mm, c d , = 2.5 mS/mm. The impulse response of the photodiodes are characterized by a linewidth (FWHM) = 70 ps and a risetime of -50 ps. The dark current in the diodes is less than 10 nA at 15 V. Furthermore, the devices show avalanche gains up to 1000 and meausrements of the impact ionization coefficients give a/P = 10 in the diode structures, which is important for low-noise operation. Microwave measurements give a gain of 8 dB at 1 GHz and anf,of 2-4 GHz, which are excellent for 1-pm gate transistors integrated with an APD. The lower value of fr. from that calcu-

lated theoretically, is due to the presence of a conducting plane ( n + contact of the photodiode) below the FET. A simplified distributed circuit analysis, showed that this partly accounts for an increase of C,, and c d , by a factor of 2 and 16.4, respectively. This problem is being investigated, and alternate techniques of integration will be discussed.

Work supported by the U.S. Army Research Office under Contract

[ I ] 0. Wada, T. Sakurai, and T. Nakagami, IEEE J . Quantum Electron.,

[2] D. Wake, E. G. Scott, and 1. D. Henning, Electron. Lett., vol. 22,

131 W. A. Hughes and D. G. Parker, Electron. Lett., vol. 22, p. 509,

DAAL-03-87-K-0007.

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1986.

IIB-6 New Quantum Well Long-Wavelength (1 = 10 pm) De- tectors and Novel Superlattice Transport Physics-B. F. Lev- ine, C. G. Bethea, J . Walker, R. J. Malik, and A. Y. Cho, AT&T Bell Laboratories, Murray Hill, NJ 07974.

Four new quantum well detector results will be discussed. We have demonstrated the first 10-pm detector based on bound

to continuum absorption in doped GaAs/AlGaAs quantum wells which have been designed to contain only one bound state. The linear voltage dependence of the responsivity is strikingly different from all our previous intersubband tunneling detectors [ l ] , [2] (containing two bound states in the quantum well) which show an exponential tunnelingQ voltage dependence. The hot electron mean free path ( L = 1700 A ) for transport above the superlattice as well as the mobility and carrier lifetime (T = 2 ps) have been deter- mined.

We have measured, for the first time, the continuous infrared ( X - 10 pm) photoconductivity spectrum, for a dual bound state in- tersubband absorption photoexcited tunneling quantum well detec- tor. The line shape is broadened and asymmetrical with respect to the zero bias Lorentzian absorption spectrum. We show that this is a result of the uncertainty principle lifetime broadening [3] due to the rapid tunneling escape of the photoexcited electrons.

We report the first intersubband absorption experiments in doped InGaAs /InAlAs multiquantum well superlattices and observe a resonance peak at a wavelength of X = 4.4 pm which is in good agreement with theory. This material system can be useful for de- tectors in the X = 3-5 pm spectra region.

We have measured a novel negative differential photoconduc- tance (at IO pm) in an alternately doped multi-quantum well struc- ture. From this measurement, the density of the electrons dynam- ically stored in the undoped wells, which is critically important in the theory of sequential tunneling [4] can be deduced at different external biases. [l] B. F. Levine, K. K. Choi, C. G. Bethea, J. Walker, and R. J. Malik,

[2] K. K. Choi, B. F. Levine, C. G. Bethea, J. Walker, and R. J. Malik,

[3] M. Tsuchiya, T. Matsusue, and H. Sakaki, Phys. Rev. Lerr., vol. 59,

[4] V. J. Goldman, D. C. Tsui, and J . E. Cunningham, Phys. Rev. Let t . ,

Appl. Phys. Lett., vol. 51, p. 934, 1987.

Phys. Rev. Lett., vol. 59, p. 2459, 1987.

p. 2356, 1987.

vol. 58, p. 1256, 1987.

IIB-7 Charge Amplification by Impact Ionization in Charge- Coupled Devices-S. A. Gajar and B. E. Burke, Lincoln Labora- tory, Massachusetts Institute of Technology, Lexington, MA 02173.

Charge-coupled device (CCD) image sensors remain limited in their ability to detect low photon fluxes by the noise of the output charge detection stage. This limitation is particularly severe at high