R. Zucca

Planar GaAs IC technology: Applications for digital LSI

This technology utilizes multiple localized ion implantations directly into semi-insulating GaAs substrates, with unimplanted areas providing isolation between circuit elements. This approach allows for high yield, high density circuits, with optimization of various types of devices (e.g., GaAs MESFETs, high-speed Schottky-barrier diodes, etc.) made possible by optimizing the implantation profile for each type of device. The application of this fabrication technology for high-speed, ultra low power digital integrated circuits using a new circuit approach called Schottky diode-FET logic (SDFL) is described. Experimental GaAS SDFL logic ICs with LSI/VLSI compatible power levels (200-500 /spl mu/W/gate) and circuit densities (<10/SUP -3/ mm/SUP 2//gate) have been fabricated.

Electrical compensation in semi‐insulating GaAs

Identification of the deep levels responsible for the electrical compensation of Cr‐doped semi‐insulating GaAs has been lacking in spite of the increasing importance of this material. Transport measurements on bulk‐grown semi‐insulating GaAs single crystals with three different Cr concentrations are presented to shed light on this problem. Alternative models for the electrical compensation are discussed. A detailed analysis of the temperature dependence of the resistivity shows that the ’’conventional’’ model in which deep Cr acceptors compensate residual shallow donors is incorrect. A more elaborate model which includes both a deep acceptor and a deep donor is proposed to properly interpret the experimental data. The deep donor level, located between 0.64 and 0.72 eV from the conduction band, is assigned to oxygen.

HgCdTe double heterostructure injection laser grown by molecular beam epitaxy

While a variety of light‐detecting devices have been made with HgCdTe, little has been done to apply this technology to light‐emitting devices. We report here the successful fabrication and operation of the first HgCdTe injection laser. This stripe‐geometry double‐heterostructure laser was operated under pulsed current at temperatures between 40 and 90 K. At 77 K, the emission wavelength was 2.86 μm with a linewidth of 0.3 meV, and the pulsed threshold current density was 625 A/cm2. The double heterostructure, with a 1.4‐μm‐thick active layer, was grown and in situ doped by molecular beam epitaxy (MBE). The p+ and n+ confinement layers were doped with arsenic and indium, respectively.

The prospects for ultrahigh-speed VLSI GaAs digital logic

Recent advances in the state of GaAs integrated circuit fabrication technology have made possible the demonstration of ultrahigh performance (\tau_{d} \sim 100ps) GaAs digital ICs with up to 64 gate MSI circuit complexities and with gate areas and power dissipations sufficiently low to make VLSI circuits achievable. It is the purpose of this paper to evaluate, based on the current state of GaAs IC technology and the fundamental device physics involved, the prospects of achieving an ultrahigh-speed VLSI GaAs IC technology. The paper includes a performance comparison analysis of Si and GaAs FETs and switching circuits which indicates that, for equivalent speed-power product operation, GaAs ICs should be about six times faster than Si ICs. The state of the art in GaAs IC fabrication and logic circuit approaches is reviewed, with particular emphasis on those approaches which are LSI/VLSI compatible in power and density. The experimental performance results are compared for the leading GaAs logic circuit approaches, both for simple ring oscillators and for more complex sequential logic circuits (which have demonstrated equivalent gate delays as low as\tau_{d} = 110ps).

Process evaluation test structures and measurement techniques for a planar GaAs digital IC technology

The successful development of a new integrated circuit (IC) technology requires a significant effort in process evaluation. This is particularly true for the high-speed low-power planar GaAs digital IC technology, which involves a relatively new semiconductor material, new processing techniques, and pursues LSI complexity using very-fine-line lithography (1-µm dimensions). This paper contains a review of the strategy employed to monitor and evaluate each of the key process steps, and to evaluate the uniformity of device parameters. The principal process evaluation test structures are discussed along with measurement techniques, and examples of measurement results are given. Our emphasis on measurement automation to facilitate the collection of a large volume of data and their statistical analysis is reflected in the paper. Examples of wafer statistics are given.

HIGH-POWER DIODE-LASER-PUMPED MIDWAVE INFRARED HGCDTE/CDZNTE QUANTUM-WELL LASERS

Diode‐array‐pumped HgCdTe/CdZnTe broad‐stripe quantum‐well lasers operated at 88 K yielded 1.3 W peak power and 10 mW average power per facet at 3.2 μm. The highest operation temperature was 154 K, and the characteristic temperature of the threshold was 16 K. The external quantum efficiency was ∼7.5% at ∼80 K and decreased by an order of magnitude at 150 K.

p‐i‐n HgCdTe photodiodes grown by molecular beam epitaxy

We report the successful molecular beam epitaxy (MBE) growth of in situ arsenic‐ and indium‐doped p‐i‐n HgCdTe double heterostructures. High‐performance, short‐wavelength, infrared (2.09 μm) photodiodes operating at 300 K have been fabricated with these double heterostructures. The observed current‐voltage characteristics and quantum efficiency of these diodes can be explained by assuming that the current components are dominated by generation‐recombination currents. These photodetectors exhibit quantum efficiencies of 78%. Growth of this kind of in situ doped structures indicates that the HgCdTe MBE technology has matured to the point where doped HgCdTe multilayer heterostructures can be grown and used to fabricate advanced infrared electronic devices.

High-power diode-pumped mid-infrared semiconductor lasers

A number of double heterostructure and quantum well lasers with wavelengths approximately 3.1, 3.2, 3.4, 3.85 - 4.1, and 4.5 micrometers have been realized in InAsSb/GaSb and HgCdTe/CdZnTe material systems. Peak powers at the few W level and average power at the few hundred mW-level were obtained from optically pumped broad-area lasers at >= 80 K. Threshold, efficiency, internal loss, and gain saturation studies are reported. A compact laser package was built, using a high-power diode array for pumping and a Stirling pump for cooling. Its performance with a 4-micrometers laser is described.

Photovoltaic effects in semi−insulating GaAs

Photovoltaic effects at junctions between semi−insulating and low−resistivity GaAs, and at Al Schottky barriers on semi−insulating GaAs are reported. Changes of photovoltage polarity as the photon energy crosses the band−gap energy are interpreted by extension of the behavior of n− and p−type GaAs.

Mutual doping effects between epitaxial ZnS films and GaAs substrates

The problem of strong self‐activated luminescence in undoped ZnS films grown on GaAs substrates by chemical vapor deposition is analyzed. Tests made by changing substrates in conjunction with photoluminescence and optical transmission measurements are described. It is concluded that mutual doping effects take place between the ZnS film and the GaAs substrate with Ga doping the ZnS films while Zn dopes the GaAs substrate.