M. T. Schmidt

Optically induced electromagnetic radiation from semiconductor surfaces

Ultrafast electromagnetic radiation induced by a femtosecond laser beam from a semiconductor provides determination of the impurity doping concentration, carrier mobility, sign, and strength of the depletion field near the semiconductor surface.

GaAs‐oxide removal using an electron cyclotron resonance hydrogen plasma

The surface chemistry of GaAs‐oxide removal with an electron cyclotron resonance (ECR) hydrogen plasma has been investigated with x‐ray photoelectron spectroscopy. It is found that As oxide is efficiently removed at room temperature, and heating expedites the removal of Ga oxide. Band bending changes during ECR hydrogen‐plasma oxide reduction are also discussed.

Diffusion-controlled distribution of solute in Sn-1% Bi specimens solidified by the submerged heater method

Abstract Two 1.35 kg, 5.8 cm diameter Sn-1% Bi specimens were solidified using the submerged heater method (SHM). The distribution of solute was found to be uniform axially, indicating that diffusion-controlled steady-state segregation, though to be unattainable on earth because of the gravity induced interference, was achieved.

Ultraviolet-light-induced oxide formation on GaAs surfaces

We present a study of deep‐ultraviolet‐light‐enhanced (4.1<hν<5.1 eV) oxygen reactions on GaAs from submonolayer to several monolayers coverage. The reaction is nonthermal and does not involve gas‐phase excitation or dissociation of O2. Our experiments show a distinct wavelength and coverage dependence for the photoenhancement. X‐ray photoelectron spectroscopy has been used to examine the chemical nature of the oxygen adsorbate and the GaAs oxides in order to find intermediate reaction species and evidence of the reaction pathways. The roles of photons and photogenerated carriers in the reaction enhancement mechanism are discussed. The results indicate that a mechanism based on photoemission of electrons into the growing oxide film is most in accord with the experimental observations. Such electron emission would increase the field‐driven transport of oxygen to the GaAs interface.

Control of the Schottky barrier using an ultrathin interface metal layer

Fermi level movements at Pt/GaAs and Ti/GaAs interfaces have been investigated using a direct measurement of Schottky barrier heights in a bimetal Schottky structure. Using thin interfacial layers, the Schottky barrier was smoothly varied from the characteristic value of the thick metal to that of the interfacial metal. The variation of barrier height versus the inner metal thickness was found to exhibit an exponential behavior extending over a few monolayers coverage. This experiment indicates a new approach to the fundamental study of metal‐semiconductor interfaces and could be useful in device applications.

Ultraviolet-light-enhanced oxidation of gallium arsenide surfaces studied by X-ray photoelectron and auger electron spectroscopy

Abstract Laser-enhanced oxidation of gallium arsenide surfaces has been investigated. The oxidation was performed either in air or in pure water at room temperature. Light at ultraviolet wavelengths was found to enhance the oxidation rate much more strongly than at visible wavelengths. The oxidation in air leaves the surface almost stoichiometric, whereas the treatment in pure water results in a gallium-rich surface.

Atomic movement during the oxidation of GaAs

Abstract A new technique is developed to study the atomic movement in ultraviolet laser enhanced and low temperature (⩽ 400 ° C) thermal oxidation of GaAs. The new method is a combination of the classical marker technique and low energy ion scattering spectroscopy (ISS). In the formation of thin GaAs oxide layers (∼ 10 A), the marker is found to remain on the oxide surface, indicating that oxidation is occurring at the intrface of GaAs/oxide by the diffusion of an oxygen species. This is in contrast to the oxidation of metals such as Ni and Cu where the same technique supports earlier observations that oxidation occurs at the oxide/ambient interface. The diffusion of a metal species results in the marker being buried during the oxidation of the metal surfaces.

The formation of elevated barrier height Schottky diodes to InP and In 0.53 Ga 0.47 AS using thin, excimer laser deposited Cd interlayers

Much recent attention has been paid to elevating the barrier height of contacts to InP and In0.53Ga0. 47As via the formation of a thin, intermediate layer between the semicon-ductor and a conventionally deposited, highly conductive contact layer. Here, we report on the use of thin (∼200Å) excimer laser photodeposited Cd as an interlayer between these semiconductors and Au overlayers in order to raise the barrier height of the re-sulting diodes. Current-voltage measurements of ideal Schottky diodes fabricated using this process yield barrier heights of 0.70 eV and 0.55 eV to InP and In0.53Ga0. 47As, re-spectively. The photodeposition process has been integrated with conventional clean room processing resulting in Au/Cd/In0.53Ga0. 47As transistors with high transconductances (∼200 mS/mm) and operating frequencies (fmax ∼ 30 GHz). X-ray photoelectron spec-troscopy of thin Cd photodeposits on InP shows that the process produces an interfacial (∼10Å thick) Cd-InP reaction zone covered by metallic Cd.

Application of photodeposited Cd to Schottky barrier diode and transistor fabrication on InP and In0.53Ga0.47As substrates

We report on using a thin (∼200 A) layer of photodeposited Cd to form high Schottky barrier height contacts to InP and In0.53Ga0.47As. Current‐voltage measurements of the Schottky diodes yield barrier heights of 0.70 and 0.55 eV to InP and In0.53Ga0.47As, respectively. The photodeposition process has been integrated with conventional clean room processing to fabricate Au/Cd/In0.53Ga0.47As transistors with high transconductances (∼200 mS/mm) and operating frequencies ( fmax∼30 GHz). X‐ray photoelectron spectroscopy of thin Cd photodeposits on InP shows that the process produces an interfacial (∼10 A thick) Cd‐InP reaction zone covered by metallic Cd.