Molecular beam heteroepitaxial growth and characterization of wide band gap semiconductor films and devices

Citation

Piquette, Eric C. (1999) Molecular beam heteroepitaxial growth and characterization of wide band gap semiconductor films and devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/by67-nr24. https://resolver.caltech.edu/CaltechETD:etd-11292006-152956

Abstract

The thesis consists of two parts. Part I describes work on the molecular beam epitaxial (MBE) growth of GaN, AlN, and Al(x)Ga(1-x)N alloys, as well as efforts in the initial technical development and demonstration of nitride-based high power electronic devices. The major issues pertaining to MBE growth are discussed, including special requirements of the growth system, substrates, film nucleation, n- and p-type doping, and the dependence of film quality on growth parameters. The GaN films were characterized by a variety of methods, including high resolution x-ray diffraction, photoluminescence, and Hall effect measurement. It is found that the film polarity and extended defect density as well as quality of photoluminescence and electrical transport properties depend crucially on how the nitride layer is nucleated on the substrate and how the subsequent film surface morphology evolves, which can be controlled by the growth conditions. A technique is proposed and demonstrated that utilizes the control of morphology evolution to reduce defect density and improve the structural quality of MBE GaN films.

In addition to growth, the design and processing of high voltage GaN Schottky diodes is presented, as well as an experimental study of sputter-deposited ohmic and rectifying metal contacts to GaN. Simple models for high power devices, based on materials properties such as minority carrier diffusion length and critical electric breakdown field, are used to estimate the voltage standoff capability, current carrying capacity, and maximum operating frequency of unipolar and bipolar GaN power devices. The materials and transport properties of GaN pertinent to high power device design were measured experimentally. High voltage Schottky rectifiers were fabricated which verify the impressive electric breakdown field of GaN (2-5 MV/cm). Electron beam induced current (EBIC) experiments were also conducted to measure the minority carrier diffusion length for both electrons and holes in GaN.

Part II of the thesis describes studies of the MBE growth of ZnS and investigations of ZnS/GaN light emitting heterojunctions which show promise for application as blue and green light emitters. Zinc sulfide layers doped with Ag and Al were grown by MBE on sapphire, GaAs, and GaN substrates and characterized by x-ray diffraction and photoluminescence. Preliminary current-voltage and electroluminescence results are presented for a processed ZnS:Al,Ag/GaN:Mg prototype blue light emitting device.

Thesis Files