Gas Source MBE and Its Use in Optoelectronics
H. Morkoc,* B. Sverdlov,* A. Salvador
U.S. Office of Naval Research, N00014-88-K-0724
(Conducted in the Coordinated Science Laboratory)

Integration of electronics and optoelectronics is expected to get the computation and signal-processing system over the present hurdle in terms of speed. New semiconductor deposition schemes from the neutral gas source and/or plasma source as well as new integration methods are being developed. The intent is to perform concept and feasibility studies. Investigations of GaSb-based heterostructures are also included in the program. Unique possibilities for bandgap engineering are provided by these heterostructures due to the extent of bandgap range and specific band-edge line-ups.

GaN is considered to be the most promising semiconductor for optoelectronic devices emitting ultraviolet and blue wavelengths because it has a large direct bandgap (Eg ~ 3.4eV), reasonable mobility (µ _300K = 600 cm²/V·s), and outstanding chemical and thermal stability. The goal of this investigation is to explore device applications of high-quality GaN grown by MBE. Short-wavelength semiconductor lasers are essential for higher density optical storage because they are limited by the diffraction of the laser wavelength and increase quadratically as the probe laser wavelength decreases. Other possible device applications include blue LEDs for full-color display technologies, high-temperature and high-power electronics in hostile environments, and sensors.

This project investigates novel classes of MISFETs based on GaAs, InGaAs, and GaN materials, which have shown promising potential in microwave and high-speed digital applications. Using state-of-the-art MBE and vacuum connected UHV CVD, the in situ deposition of Si₃N₄ layers is performed on compound semiconductors for these MISFETs, without any significant contamination. The insertion of a thin layer of Si between the Si₃N₄ and GaAs allows the interface quality to be greatly improved. The research is directed to a solution for inversion-mode and enhanced-mode devices compatible with the traditional IC processing technologies.

This project investigates dielectrics deposited in situ (SiO₂, Si₃N₄, and others) in a UHV environment on a variety of commercially important semiconductors: Si, GaAs, and InP. The choice of this particular environment is twofold. One is that the control of the environment is of paramount importance to delineate phenomena from contamination. Second, our process is adaptable to an industrial setting either as an MBE/UHVCVD setup or an OMVPE/UHVCVD apparatus. Electrical measurements, such as capacitance-voltage and current-voltage, and other measurements such as STM and XPS, are performed for the analysis of dielectric/semiconductor interfaces. The aim is to obtain deposited insulators and insulator/semiconductor interfaces of a quality suitable for electronic devices.

This project explores the structural and electrical properties of the interface between insulator and semiconductor to develop a viable III-V compound semiconductor-based metal-insulator-semiconductor (MIS) device for high-speed applications in semiconductor heterojunctions and semiconductor-insulator systems. Their optimum combination for novel devices such as an MIS diode and field-effect transistor is also explored. The structural analysis employs TEM, x-ray diffractometer, and in situ STM and XPS. Electrical measurements include such techniques as C-V and G/w-V for the interface characterization.