T. C. McGill

Oscillations up to 712 GHz in InAs/AlSb resonant‐tunneling diodes

Oscillations have been obtained at frequencies from 100 to 712 GHz in InAs/AlSb double‐barrier resonant‐tunneling diodes at room temperature. The measured power density at 360 GHz was 90 W cm−2, which is 50 times that generated by GaAs/AlAs diodes at essentially the same frequency. The oscillation at 712 GHz represents the highest frequency reported to date from a solid‐state electronic oscillator at room temperature.

New negative differential resistance device based on resonant interband tunneling

We propose and demonstrate a novel negative differential resistance device based on resonant interband tunneling. Electrons in the InAs/AlSb/GaSb/AlSb/InAs structure tunnel from the InAs conduction band into a quantized state in the GaSb valence band, giving rise to a peak in the current-voltage characteristic. This heterostructure design virtually eliminates many of the competing transport mechanisms which limit the performance of conventional double-barrier structures. Peak-to-valley current ratios as high as 20 and 88 are observed at room temperature and liquid-nitrogen temperature, respectively. These are the highest values reported for any tunnel structure.

Lattice match: An application to heteroepitaxy

We define the concept of lattice match for any pair of crystal lattices in any given crystal direction, allowing for a periodic reconstruction of the interface. An algorithm for a systematic search for all possible matches is developed, and some examples of nonstandard lattice matches are given for CdTe on GaAs and sapphire to illustrate the method. For the case of CdTe on GaAs, our results agree with published results, both with respect to growth plane and orientation for CdTe(111) on GaAs(100). For CdTe on sapphire, our results agree with published results with respect to growth plane.

The CdTe/HgTe superlattice: Proposal for a new infrared material

We propose a new material which could be useful in a number of infrared optoelectronic devices. The material consists of alternating (100) layers of CdTe and HgTe. The band gap of this superlattice is adjustable from 0 to 1.6 eV depending on the thicknesses of the CdTe and HgTe layers. Details of the band‐gap variation and the character of the band‐edge states are presented.

High voltage (450 V) GaN Schottky rectifiers

We fabricated high standoff voltage (450 V) Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm2 and a saturation current density of 10^–5 A/cm2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2 ± 0.7) × 10^6 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects.

Advantages of the HgTe‐CdTe superlattice as an infrared detector material

The HgTe‐CdTe superlattice is found to exhibit properties superior to those of the (Hg, Cd)Te alloy as an infrared detector material. A calculation shows that the superlattice tunneling length is shorter than that of the alloy with the same band gap. For a given cutoff wavelength tolerance, we find that less fractional precision is needed in the superlattice control parameter (layer thicknesses) than in the alloy control parameter (composition). Also, p‐side diffusion currents are expected to be reduced due to the larger superlattice electron effective mass.

Minority carrier diffusion length and lifetime in GaN

Electron beam induced current measurements on planar Schottky diodes on undoped GaN grown by metalorganic chemical vapor deposition are reported. The minority carrier diffusion length of 0.28 μm has been measured, indicating minority carrier lifetime of 6.5 ns. The tapping mode atomic force microscopy imaging of the surfaces and scanning electron microscopy of the cross sections have been used to characterize the linear dislocations and columnar structure of the GaN. The possible influence of recombination on the extended defects in GaN on the minority carrier diffusion length and lifetime is discussed, and contrasted to other recombination mechanisms.

Stability of cerium oxide on silicon studied by x-ray photoelectron spectroscopy

The silicon-cerium oxide interface is studied using x-ray photoelectron spectroscopy. The oxidation and reduction of species at the interface are examined as a function of annealing temperature both in vacuum and oxygen ambient, in order to determine their relative stabilities. By depositing a very thin CeO2 film (similar to 30 Angstrom), the cerium and silicon core level peaks can be monitored simultaneously. The presence of characteristic chemical shifts of the Si 2p peak gives information about any SiOx, layer that may form at the interface. The oxidation state of the cerium can be probed from three different areas of the spectrum. From this information we can infer the oxidation state of both the silicon and the cerium. For the first time a complete picture of the interface is obtained. The implications of these findings on the utility of CeO2 in device applications are discussed.

Variation of impurity−to−band activation energies with impurity density

A theory of the variation of conduction electron density with the temperature for various impurity concentrations is presented. In addition to previously noted effects of condcution band edge lowering and screening of the impurity potential by the conduction electrons, the influence of a finite energy transfer integral and spatial fluctuation in the potential are included. The results show that for ND ~ ≥ 10^(17) cm^–3 in silicon one must not view the activation as occurring between a single impurity level and a well–defined conduction band edge, but must include the broadening of the impurity level and tailing of the conduction–band density of states. Calculations for the shallow donors P, Sb, and As in Si are found to be in satisfactory agreement with experiment.

Electron diffusion length and lifetime in p-type GaN

We report on electron beam induced current and current–voltage (I–V) measurements on Schottky diodes on p-type doped GaN layers grown by metal organic chemical vapor deposition. A Schottky barrier height of 0.9 eV was measured for the Ti/Au Schottky contact from the I–V data. A minority carrier diffusion length for electrons of (0.2 ± 0.05) µm was measured for the first time in GaN. This diffusion length corresponds to an electron lifetime of approximately 0.1 ns. We attempted to correlate the measured electron diffusion length and lifetime with several possible recombination mechanisms in GaN and establish connection with electronic and structural properties of GaN.