R. Ludeke

Molecular‐beam epitaxy (MBE) of In1−xGaxAs and GaSb1−yAsy

Films of In1−xGaxAs and GaSb1−yAsy over the entire composition ranges have been grown on (100) GaAs, InAs, and GaSb substrates by MBE. In situ observations by high‐energy electron diffraction have revealed a variety of surface reconstructions and correlated the growth process with the lattice mismatch. The compositions are governed by the relative rates of In and Ga in In1−xGaxAs, but primarily by that of Sb in GaSb1−yAsy because of its dominant incorporation over As. In these alloys, Sn is found to be a donor throughout In1−xGaxAs but an amphoteric impurity in GaSb1−yAsy.

In1−xGaxAs‐GaSb1−yAsy heterojunctions by molecular beam epitaxy

Smooth films of n‐In1−xGaxAs and p‐GaSb1−yAsy were grown by molecular beam epitaxy. As a function of the compositions, x and y, the lattice constants vary linearly while the energy gaps show a downward bowing. Abrupt heterojunctions made of these alloys with close lattice matching exhibit a series of current‐voltage characteristics which change from rectifying to Ohmic as x and y are reduced. The relative location of the band‐edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally.

Local transport and trapping issues in Al2O3 gate oxide structures

The bias dependence of interfacial barriers in Al2O3-based metal–oxide–semiconductor structures was studied by ballistic electron emission spectroscopy. Strong image force reductions of the barriers were observed. A conduction band offset between Al2O3 and Si of 2.78 eV was obtained. Electron trapping into levels that overlap the Si band gap and are located near the Si–Al2O3 interface led to charge densities of ∼2.5×1012 cm−2.

Molecular beam epitaxy of alternating metal‐semiconductor films

Alternately repeated layers of metal epitaxy on semiconductor substrates and semiconductor epitaxy on metal substrates are grown in an ultra-high vacuum evaporation system by first depositing the metal film on the clean surface of the semiconductor substrate over the temperature range between room temperature and 400 DEG C; and then depositing the semiconductor film on the clean surface of the metal over the temperature range between 500 DEG C and 600 DEG C.

Observation of semiconductor‐semimetal transition in InAs‐GaSb superlattices

The semiconductor‐semimetal transition in InAs‐GaSb superlattices is observed at a layer thickness in the vicinity of 100 A. The transition manifests itself in an increase in the measured carrier concentration as a result of electron transfer from GaSb to InAs when ground subbands of electrons and heavy holes cross each other. Shubnikov‐de Haas measurements confirm the carrier enhancement in the semimetallic state.

Ga1−x Alx As superlattices profiled by Auger electron spectroscopy

Superlattice structures made by molecular beam epitaxy are profiled by a combined technique of argon sputter etching and Auger electron spectroscopy. The superlattice, consisting of periodic layers of 50‐A GaAs and Ga1−xAlxAs, probably represents the structure with the shortest period ever made and analyzed in monocrystalline semiconductors. Also established is the dependence of the intensity ratio of aluminum to arsenic signals of Auger transitions on the aluminum composition in Ga1−xAlxAs.

Tunable GaAs Laser in an External Dispersive Cavity

Tunability of the cw radiation from a GaAs injection laser in an external dispersive cavity was achieved over a range of 150 A about a center wavelength of 8525 A at 77°K. The emitted radiation was analyzed with a Fabry‐Perot etalon. Under certain conditions single‐mode operation with cw output power as large as 17 mW was observed. Half‐width of such modes was estimated to be less than 350 MHz.

Ion backscattering and channeling study of InAs‐GaSb superlattices

We show that the Rutherford backscattering yield from [100] InAs‐GaSb superlattices has a marked oscillatory structure indicative of the superlattice periodicity. Channeling measurements reveal higher dechanneling along 〈110〉 than along [100] directions, and this can be interpreted as an evidence for relaxation effects along the [100] growth direction at each InAs‐GaSb interface. We attribute this to the fact that, although there is a good lattice match between InAs and GaSb, the interfaces consist of either Ga–As or In–Sb bonds, which differ by 7% in binding distance from InAs‐GaSb.

Hot electron transport in SiO2 probed with a scanning tunnel microscope

Hot electrons injected with a scanning tunnel microscope (STM) tip into Pt/SiO2/Si(100) structures were detected as a collector current in the Si by using a STM configuration known as ballistic electron emission microscopy. The collector current, observed for STM tip potentials ≳4 V and for oxide biases ≥0 V, is direct evidence for electron transmission through the conduction band of the SiO2. Negative oxide biases delayed the onset of current to correspondingly higher tip potentials. A simple model was used to extract the energy and bias dependent transmission probabilities from the experimental data for a 62 A SiO2 layer. The results are compared with Monte Carlo calculations.

Determination of the energy-dependent conduction band mass in SiO2

The energy dependence of the conduction band mass in amorphous SiO2 was deduced from quantum interference oscillations in the ballistic electron emission microscope current, and separately from Monte Carlo simulations of the electron mean free paths obtained by internal photoemission. The results imply a strong nonparabolicity of the conduction band of SiO2.