George David Pettit

Bio: George David Pettit is an academic researcher from IBM. The author has contributed to research in topics: Schottky barrier & Fermi level. The author has an hindex of 35, co-authored 131 publications receiving 4664 citations.

Nucleation mechanisms and the elimination of misfit dislocations at mismatched interfaces by reduction in growth area

Abstract: To investigate the effect of growth area on interface dislocation density in strained‐layer epitaxy, we have fabricated 2‐μm‐high mesas of varying lateral dimensions and geometry in (001) GaAs substrates with dislocation densities of 1.5×105, 104, and 102 cm−2. 3500‐, 7000‐, and 8250‐A‐thick In0.05Ga0.95As layers, corresponding to 5, 10, and 11 times the experimental critical layer thickness as measured for large‐area samples, were then deposited by molecular‐beam epitaxy. For the 3500‐A layers, the linear interface dislocation density, defined as the inverse of the average dislocation spacing, was reduced from greater than 5000 to less than 800 cm−1 for mesas as large as 100 μm. A pronounced difference in the linear interface dislocation densities along the two interface 〈110〉 directions indicates that α dislocations nucleate about twice as much as β dislocations. For samples grown on the highest dislocation density substrates, the linear interface‐dislocation density was found to vary linearly with mesa...

Unpinned (100) GaAs surfaces in air using photochemistry

Abstract: We have unpinned the Fermi level at the surface of both n‐ and p‐type (100) GaAs in air. Light‐induced photochemistry between GaAs and water unpins the surface Fermi level by reducing the surface state density. Excitation photoluminescence spectroscopy shows a substantial decrease in both surface band bending and surface recombination velocity in treated samples, consistent with a greatly reduced surface state density (≂1011 cm−2). Capacitance‐voltage measurements on metal‐insulator‐semiconductor structures corroborate this reduction in surface state density and show that the band bending may be controlled externally, indicating an unpinned Fermi level at the insulator/GaAs interface. We discuss a possible unpinning mechanism.

Ohmic contacts to n‐GaAs using graded band gap layers of Ga1−xInxAs grown by molecular beam epitaxy

Abstract: Ohmic contacts were studied on structures which utilize the fact that for InAs surfaces Fermi level pinning occurs at or in the conduction band. It was found that an epitaxial layer of n‐Ga1−xInxAs grown by molecular beam epitaxy on n‐GaAs which is graded in composition from x = 0 at the GaAs interface to 0.8?x?1.0 at the surface will produce a structure with a nearly zero Schottky barrier height for the metal–Ga1−xInxAs interface and hence a low resistance ohmic contact. A transmission line measurement of non‐alloyed contact resistance of 5×10−7

An In 0.15 Ga 0.85 As/GaAs pseudomorphic single quantum well HEMT

Abstract: This letter describes high electron mobility transistors (HEMT's) utilizing a conducting channel which is a single In 0.15 Ga 0.85 AS quantum well grown pseudomorphically on a GaAs substrate. A Hall mobility of 40 000 cm2/V.s has been observed at 77 K. Shubnikov-de Haas oscillations have been observed at 4.2 K which verify the existence of a two-dimensional electron gas at the In 0.15 Ga 0.85 As/GaAs interface. HEMT's fabricated with 2-µm gate lengths show an extrinsic transconductance of 90 and 140 mS/mm at 300 and 77 K, respectively-significantly larger than that previously reported for strained-layer superlattice In x Ga 1-x As structures which are nonpseudomorphic to GaAs substrates. HEMT's with 1-µm gate lengths have been fabricated, which show an extrinsic transconductance of 175 mS/mm at 300 K which is higher than previously reported values for both strained and unstrained In x Ga 1-x As FET's. The absence of Al x Ga 1-x As in these structures has eliminated both the persistent photoconductivity effect and drain current collapse at 77 K.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Dielectric functions and optical parameters of Si, Ge, GaP, GaAs, GaSb, InP, InAs, and InSb from 1.5 to 6.0 eV

Abstract: We report values of pseudodielectric functions $〈\ensuremath{\epsilon}〉=〈{\ensuremath{\epsilon}}_{1}〉+i〈{\ensuremath{\epsilon}}_{2}〉$ measured by spectroscopic ellipsometry and refractive indices $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}=n+ik$, reflectivities $R$, and absorption coefficients $\ensuremath{\alpha}$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ in optical measurements.

Reversible conductivity changes in discharge‐produced amorphous Si

Abstract: A new reversible photoelectronic effect is reported for amorphous Si produced by glow discharge of SiH4. Long exposure to light decreases both the photoconductivity and the dark conductivity, the latter by nearly four orders of magnitude. Annealing above 150 °C reverses the process. A model involving optically induced changes in gap states is proposed. The results have strong implications for both the physical nature of the material and for its applications in thin‐film solar cells, as well as the reproducibility of measurements on discharge‐produced Si.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

Abstract: 1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.