This proposal describes research on novel structures and metallizations for wide bandgap semiconductor devices, the development of integrated laboratory-classroom modules associated with semiconductors and thin film science, and the extension of coordinated advising and outreach activities.
Due to its large bandgap (3.4 eV), high thermal conductivity, and high saturation drift velocity, gallium nitride is being intensively pursued for a variety of optoelectronic and high temperature, high frequency, and high power electronic devices. Recent advances in the quality of GaN epitaxial films have prompted efforts to develop structures which can be used in making efficient devices. In this project novel structures comprising conducting layers and semiconducting GaN films will be investigated. This work will employ the selective growth of GaN and its subsequent overgrowth to produce embedded conducting layers (ECL) within the GaN epitaxial films. These structures will have potential applications in devices such as ultra-violet photodetectors and permeable base transistors.
A closely related challenge for the development of both GaN and SiC devices involves the fabrication of p-type ohmic contacts with low specific contact resistivities (SCRs). Because of the large bandgaps and large workfunctions of these semiconductors, metal contacts on p-type material yield large Schottky barrier heights, or energy barriers for electron transport across the metal-semiconductor interface. These large barrier heights increase SCRs even on relatively highly doped material. To reduce the Schottky barrier heights InxGa1-xN will be investigated in the form of thin (~50-100 A) interlayers between selected metal contacts and the p-type GaN or SiC semiconductor substrates. Indium nitride and gallium nitride are completely soluble in one another, such that the composition of InxGa1-xN may be varied over the range from pure GaN to pure InN. By varying the composition, and thus the bandgap, of the lnxGal-XN interlayer, it is believed that the barrier heights can be significantly reduced.
The long-term outlook for the advancement of wide bandgap semiconductor technology will depend on the availability of suitably educated graduates. Recent research indicates that students learn best when laboratory courses are integrated with classroom experiences. For this reason the Materials Science & Engineering Department at CMU plans to implement a new undergraduate curriculum with extensive integration of laboratory and classroom courses. The development of instructive experiments will be critically important to the successful implementation of this program. This proposal discusses plans for developing selected laboratory modules and expanding student advising and outreach programs. ***
