Electrical and Computer Engineering ETDs

Publication Date

12-1-1973

Abstract

This work covers the most important basic facts about the thermal oxidation of gallium arsenide phosphide. The work is confined to lightly dopes GaAs(1-x)^px material with a phosphorus mole fraction of 0.50+-0.02. All oxidations were carried out in open tubes and consequently at atm

ospheric pressure. Initial studies over a wide range of oxidation temper­atures showed that serious surface damage to the semiconductor surface occurred if the oxidation temperature was greater than 700° C. An anneal in an inert atmosphere at a temperature no greater than 700° C for at least 90 minutes was required to obtain good pinhole-free dielectrics. The film is neither single crystal nor amorphous but is composed of very small (<1/2 micron) diameter crystallites.

Growth speed of the film at temperatures near 700° C was measured. The dielectric constant of the film was measured as 2.77±0.66. The film can be photomasked and selectively etched with conventional Kodak nega­tive photoresist techniques. Selective etching of a photoresist defined pattern was studied; a number of etches were tried, NH4F was the best. Its rate was predictable and it did not attack the semiconductor surface.

The upper bound on the oxidation temperature was found to be explainedby arsenic sublimation as As2 and As4 molecules and by phosphorus sublimation as P2 molecules. Theory is developed for the growth of volatile-element-free pits in the semiconductor surface. The rapid increase of pitting at temperatures above 700°C is explained by a very rapid increase in arsenic and phosphorus vapor pressures in this temperature range. The sublimation value is too slow to be a limiting condition on the growth rate of the insulator.

Two separate techniques were emploted to identify the relative proportions of Ga2O3 and GaPO4.

The insulator film was shown to be B-Ga2O3 and berlinite-type GaPO4. Relative concentrations of the two compounds were obtained by two completely independent experiments. First, the film atoms were excited by low-energy electrons from the beam of a scanning electron beam microscope and characteristic X-rays for various species were counted. Second, the film was also studied by backscattered energy spectra of a 2 MeV a­particle beam. Data reduction of both techniques is fully described. Both experiments led to a molecular formula for the film of 3GaPO4 + 2Ga2O3.

The ion backscattering experiment also showed the existence of a disordered layer below the insulator film. This layer helped explain otherwise anomalous results obtained with metal insulator semiconductor (MIS) capacitors made with the metal-GaPO4/Ga2O3-GaAs1/2P1/2 structure.

Capacitance vs voltage data were obtained from a large number of MIS capacitors. Theoretical C-V curves for this insulator-semiconductor combination were calculated and compared with experimental curves. Ex­perimental curves depart from theoretical curves when the semiconductor is reverse biased, and no surface inversion is seen. The steady-state depletion mode is explained by the low minority carrier generation rate in the space charge layer of the wide bandgap semiconductor.

Document Type

Dissertation

Language

English

Degree Name

Electrical Engineering

Level of Degree

Doctoral

Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Wayne Willis Grannemann

Second Committee Member

Harold Dean Southward

Third Committee Member

Lewellyn Boatwright Jr

Fourth Committee Member

William Jackson Byatt

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