Recent advances in monolithic semiconductor technology at W- band (75 to 110 GHz) have enabled implementation of compact radiometer front-ends for imaging applications. This paper describes a downconversion approach using Gallium Arsenide (GaAs) monolithic microwave/millimeter-wave integrated circuits (MMIC) to build modules for a 32-element receiver array. The MMIC downconverter module contains low noise amplifiers (LNA), microstrip bandpass filter, Schottky diode mixer and IF amplifiers. In conjunction with the local oscillator (LO), each downconverter serves as a superheterodyne receiver channel in the imaging array. The W- band array has 32 downconverter modules and 8 LO distribution modules which distribute LO power from a Gunn diode oscillator to each downconverter. The LO distribution module incorporates varactor phase shifters with LO drive amplifiers for phase adjustments of plus or minus 180 degrees to match the phase output from each receiver channel. The downconverter modules of the 32-element array demonstrated greater than 40 dB RF-to- IF gain and an average noise figure of 5.7 dB over a 10 GHz bandwidth centered at 94 GHz. Uniformity of the MMIC devices allows gain tracking within plus or minus 2.5 dB and phase tracking within plus or minus 18 degrees between the 32 receive channels. For Dicke radiometer operation, a PIN diode switch MMIC has been inserted in front of LNA in the downconverter module. Noise figure and gain results for the PIN switch front-end will be presented.

This letter describes the material characterization and device test of InAlAsDnGaAs high electron mobility tran- sistors (HEMT's) grown on GaAs substrates with indium com- positions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered pro- duction cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of p = 10000 cm2Ns, n = 3.2 x lo1' cmp2 (In = 53%) and p = 11800 cm2Ns, n = 2.8 x 10 cm-' (In = 60%). A series of In = 53%' 0.1 x 100pm' and 0.1 x 50pm2 devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1 x 50pm2 discrete HEMT's up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconduc- tance (gm,i) of 1.67 S/mm, with unity current gain frequency (fT) of 150 GHz and a maximum frequency of oscillation (fInax) of 330 GHz. Transistors with In = 60% exhibited an extrinsic gm of 1.7 S/mm, which is the highest reported value for a GaAs based device.

This letter describes the material characterization and device test of InAlAs/InGaAs high electron mobility transistors (HEMT's) grown on GaAs substrates with indium compositions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered production cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of mu = 10000 cm(2)/Vs, n = 3.2 x 10(12) cm(-2) (In = 53%) and mu = 11 800 cm(2)/Vs, n = 2.8 x 10(12) cm(-2) (In = 60%). A series of In = 53%, 0.1 x 100 mu m(2) and 0.1 x 50 mu m(2) devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1 x 50 mu m(2) discrete HEMT's up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconductance (g(m, i)) of 1.67 S/mm, with unity current gain frequency (f(T)) of 150 GHz and a maximum frequency of oscillation (f(max)) of 330 GHz. Transistors with In = 60% exhibited an extrinsic g(m) of 1.7 S/mm, which is the highest reported value for a GaAs based device.

The first 94 GHz receive active phased array providing electronically scannable monopulse patterns in two orthogonal planes has been fabricated and tested. State of the art performance has been achieved. Beamwidths of 2.3 degrees and peak to null ratios of 20 dB have been recorded.

Multichip monolithic-integrated circuit modules that provide low-noise amplification, bandpass filtering, square-law detection, and DC amplification of a broadband millimeter-wave signal are described. The module is compact (4.50 cm/sup 3/) and lightweight (37 g), has low power consumption (80-130 mW), and is well-suited for use in focal-plane arrays to provide passive imaging of millimeter-wave thermal radiation. The theoretical gain requirement, radiometer construction, and measured results are reported.<>

A compact (1.8 by 3.0 by 3.8 cm) WR-10 waveguide amplifier module providing 310-mW power output, 20-dB gain, and 5 GHz of 1-dB bandwidth at a center frequency of 96 GHz is described. The module is comprised of 22 identical PHEMT chips, 4-way microstrip power combiners and dividers, and a 4-way waveguide power combiner.<>

Five versions of monolithic W-band 0.1 mu m A1GaAs/InGaAs/GaAs pseudomorphic High Electron Mobility Transistor, four-stage, Low Noise Amplifiers based on two different designs were developed. These millimeter wave monolithic integrated circuits have produced a minimum noise figure of 3.5 dB with 23.0 dB gain at 92 GHz and a maximum gain of 33.5 dB with a 6.2 dB noise figure at 102 GHz. This is the highest gain yet reported for a single chip W-band amplifier. The chips feature coplanar waveguide circuit elements and compact size for low-cost production, single-polarity bias requirement, and a minimum of DC bonding pads.

Two monolithic W-band four-stage LNA's based on 0.1 /spl mu/m AlGaAs-InGaAs-GaAs p-HEMT technology were developed. One with integral waveguide coupling probes has achieved a noise figure of 4.0 dB with a gain of 30.8 dB at 94 GHz; the other has a gain of 31.7 dB with a noise figure of 5.9 dB at 102 GHz. This is the highest gain yet reported for a single chip W-band amplifier. The chips features CPW circuit elements and compact size for low-cost production, single-polarity bias requirement, and a minimum of DC bonding pads.<>

A monolithic, three-stage W-band power amplifier, developed using pseudomorphic HEMTs, has exhibited record gain, power per unit gate width, and power per unit area. The amplifier has a small signal gain of 22-dB and an output power of 37-mW with an associated gain of 10-dB. A three-stage V-band power amplifier with record gain and power per unit area has also been fabricated on the same wafer with a small signal gain of 16-dB and an output power of 112-mW with an associated gain of 8-dB.<>

Monolithic W-band amplifiers and a novel W-band mixer fabricated using a 0.1 mu m pseudomorphic MODFET technology are presented. Single-stage W-band amplifiers delivered 8.5-dB gain; four-stage units showed 23-dB maximum gain or 4.5-dB noise figure, 21.7-dB associated gain. Monolithic W-band mixers have shown 11.8 dB conversion loss.<>

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation G. D. Davis, N. E. Byer, R. A. Riedel, G. Margaritondo; Summary Abstract: Deposition of Al overlayers onto cleaved (HgCd)Te surfaces. Journal of Vacuum Science & Technology A 1 May 1985; 3 (3): 981–982. https://doi.org/10.1116/1.573370 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAVS: Science & Technology of Materials Interfaces and ProcessingJournal of Vacuum Science & Technology A Search Advanced Search |Citation Search

The reaction of the cleaved Hg0.72Cd0.28Te surface with atomic hyrogen has been studied with ultraviolet photoelectron spectra obtained using synchrotron radiation. Hydrogen exposures of 600 L or less caused no detectable difference in the photoelectron spectra. However, dramatic changes were observed upon extended hydrogenation with the mercury signal decreasing to ∼20% of its original value before the surface passivated at an exposure of l04 L with the apparent formation of hydrogen– Hg and Cd complexes. During hydrogenation, some of the freed Hg diffuses into the semiconductor to form a degenerate n-type surface layer. This process is contrasted to oxidation where no saturation of the surface was seen and the reacted surface was almost completely Hg free.

The interactions between the clean, cleaved Hg0.72Cd0.28Te surfaces and thin evaporated layers of Al and In have been investigated with ultraviolet photoelectron spectroscopy using synchrotron radiation. Deposition of ultrathin layers of either metal was found to deplete the surface of much of its Hg by breaking the Hg-Te bonds to form a very thin interlayer of Al2Te3 or one of the several indium tellurides. In contrast, no interaction between the metals and the CdTe component was observed. Upon deposition of additional Al, a metallic Al overlayer was grown, with some Te diffusing to the surface. Some of the Hg freed by the initial reaction diffused into the semiconductor and formed a degenerate n+ layer capable of ohmically coupling n-type material to the metallic overlayer.

Cross-sectional transmission electron microscopy was used to determine the growth kinetics of silicide films in the Cr/(100)Si system. Growth rate, growth mechanisms, and structural details were obtained from direct observation of the reacted layer after various time intervals. At 425 °C, CrSi2 was the only phase formed; its growth was diffusion-limited, with a rate constant of 6.2×10−13 cm2/s. A thin oxide layer (∼20 Å) at the Cr/Si interface did not prevent silicide growth at 425 °C, but it served as an immobile marker, which confirmed that Si was the main diffusing species.

Recent work has demonstrated that light can be used to both phase-lock and switch IMPATT diodes. However, because the light that was used has energy E higher than band gap Ea, it cannot effectively reach the deeply-buried active region of the diode. The result hds been low optical coupling efficiencies (< 2%). We find that Burstein shift and internal photoemission can be used to enhance the efficiency by tuning E around Eg. These two mechanisms also can be used to define a better phase relationship with the locked microwaves with adjusting the distribution of photoinduced current injected into the active region. Our photoresponse study of Ti/W-GaAs Schottky IMPATT diodes has shown that efficiencies can be increased to 50% and 13% at E = 1.42 eV (using Burstein shift) and 1.38 eV (using internal photoemission), respectively. In the former case, the current is generated over the entire active region. In the latter case, the current is injected from a narrow region, i.e., the junction area.

The interaction of evaporated Au overlayers with ultrahigh vacuum-cleaved p-type Hg0.72Cd0.28Te(110) surfaces has been studied with ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. For all coverages of Au, a significant out-diffusion of Te occurs so that the cation-to-anion ratio [(Hg+Cd)/Te] decreases from 1.0 for the clean surface to 0.2 for 30 Å of Au and to 0.03 for 100 Å of Au. In contrast to the behavior previously observed following Al deposition, the Hg/Cd ratio remains constant at low coverages although it decreases to ∼70% of the initial value for thicker Au layers (20–50 Å). During the initial stages of deposition, the band bending changes from the inverted state present after cleavage toward flat band or accumulation. This behavior, probably due to in-diffusion of Au, is consistent with the use of Au as an Ohmic contact with p-type material.

It has been shown previously that tunneling current can become the dominant dark current and hence the performance-limiting factor in diodes formed in narrow bandgap semiconductors, such as Hg1_xCdxTe. In this paper, we calculate the tunneling current using a Kane approximation for the nonparabolic conduction band and a more realistic junction potential than has been used previously. The potential used here is characteristic of a linearly graded n-type region intersecting a uniformly doped p-type region and is a better approximation to the actual potential in a diode formed by ion implantation into a p-type substrate. We show that significant errors sometimes arise when the abrupt junction model is used to calculate tunneling current in these structures. The effect of changes in base carrier concentration and n-side donor gradient is shown forxbetween 0.196 and 0.400, which corresponds to a photodiode spectral cutoff in the important 3- to 14-µm region.