Gary Y. Robinson

Epitaxial films of semiconducting FeSi2 on (001) silicon

Epitaxial thin films of the semiconducting transition metal silicide, beta‐FeSi2, were grown on (001) silicon wafers. The observed matching face relationship is FeSi2(100)/Si(001), with the azimuthal orientation being FeSi2[010]‖‖Si〈110〉. This heteroepitaxial relationship has a common unit mesh of 59 A2 area, with a mismatch of 2.1%. There is a strong tendency toward island formation within this heteroepitaxial system.

110-GHz GaInAs/InP double heterostructure p-i-n photodetectors

Long-wavelength GaInAs/InP graded double heterostructure p-i-n photodiodes are demonstrated with 3-dB bandwidths over 100 GHz. The heterojunction hole trapping problem is significantly improved and the device contact resistivity is greatly reduced by using superlattice graded bandgap layers at the hetero-interfaces to reduce the barrier height. Self-aligned processes are used in the device fabrication to reduce device parasitics. Pulsewidths as short as 3.0 ps full-width-at-its-half-maximum (FWHM) for 2 /spl mu/m/spl times/2 /spl mu/m device are measured by pump-probe electrooptic sampling. 3-dB bandwidths over 100 GHz are found for 2 /spl mu/m/spl times/2 /spl mu/m and 3 /spl mu/m/spl times/3 /spl mu/m devices. The device with the integrated bias tee can be biased without using the external bias tee. The electrical resonance between the photodiode and external circuits was reduced by integrating an impedance matched resistor in parallel with the photodiode. The 7 /spl mu/m/spl times/7 /spl mu/m device with bias tee and matched resistor has a measured pulsewidth of 3.8 ps and a 3-dB bandwidth over 100 GHz. The calculated pulse shape based on the saturation velocity model fits well with the measured response. A model for different components of the series resistance agrees with the measured area dependence of the series resistance. >

A review of the geometrical fundamentals of reflection high‐energy electron diffraction with application to silicon surfaces

Reflection high‐energy electron diffraction (RHEED) is an experimentally simple technique, and yet a powerful one for examining the structure of a substrate surface and for monitoring the surface crystal structure and the crystallographic orientation of thin films during their growth. However, it can be difficult to learn to interpret the RHEED patterns of new materials, because a practical and adequately detailed introduction to the technique is not generally available. To address this need, we develop the geometrical principles of RHEED; using the kinematic approximation, we show how a particular point of the sample surface’s reciprocal net gives rise to a diffraction maximum at a particular location on the RHEED viewing screen. We explain the origins of ‘‘reciprocal lattice rods,’’ RHEED streaks, and Laue rings. We show how to calculate the streak spacing, and clarify the basic effect on the RHEED pattern of using a nonzero angle of incidence for the incident beam. Crystalline nets, reciprocal nets, an...

Electrical and optical feedback in an InGaAs/InP light-amplifying optical switch (LAOS)

A circuit model for optical and electrical feedback has been developed to investigate the cause of negative differential resistance (NDR) switching in a series connected heterojunction phototransistor (HPT) light-emitting diode (LED) device. The model considers optical feedback from the light generated in the LED, electrical feedback from the holes thermally emitted over the LED cladding layer, nonlinear gain of the HPT, the Early effect, and leakage resistance. The analysis shows that either electrical or optical feedback can be the dominant cause for the NDR, depending upon their relative strengths. The NDR observed in the devices was caused primarily by electrical feedback since the optical feedback is weak. For low input power, avalanche breakdown appears to initiate the NDR in the devices although avalanching alone cannot cause NDR. >

Schottky Diodes and Ohmic Contacts for the III-V Semiconductors

In this chapter a review of the electrical properties of metal-semiconductor contacts to the III-V semiconductors is given. Metal-semiconductor structures play an important role in devices based on the III-V compound semiconductors in the form of Schottky-barrier diodes or ohmic contacts. Important III-V devices utilizing Schottky-barrier junctions include solar cells, microwave mixer diodes, and metal semiconductor field-effect transistors (MESFETs) and their associated integrated circuits. Schottky diodes also find widespread use for III-V semiconductor materials characterization, including carrier concentration profiling and deep-level identification. Ohmic contacts with low resistance are necessary for high performance in many III-V devices. For example, the efficiency of light-emitting diodes and lasers is strongly influenced by contact resistance, and the noise behavior and the gain of an FET are significantly affected by the character of ohmic contacts. In all of these cases, the metal-semiconductor interface is formed on a chemically etched, as compared to an atomically clean, semiconductor surface. Thus, in this chapter the properties of Schottky diodes and ohmic contacts prepared by chemically etching the III-V semiconductors are emphasized, while the previous chapter dealt with metal-semiconductor interface formation on atomically clean surfaces.

Epitaxial tendencies of ReSi2 on (001) silicon

ReSi2 thin films were grown on (001) silicon wafers by vacuum evaporation of rhenium onto hot substrates in ultrahigh vacuum. The preferred epitaxial relationship was found to be ReSi2 (100)/Si(001) with ReSi2 [010]∥Si〈110〉. The lattice matching consists of a common unit mesh of 120 A2 area, and a mismatch of 1.8%. Transmission electron microscopy revealed the existence of rotation twins corresponding to two distinct but equivalent azimuthal orientations of the common unit mesh. Although the lateral dimension of the twins is on the order of 100 A, MeV He+ backscattering spectrometry revealed a minimum channeling yield of 2% for a ∼1500‐A‐thick film grown at 650u2009°C. There is a very high degree of alignment between the ReSi2 (100) and the Si(001) planes.

Gas‐source molecular‐beam epitaxy growth of InxGa1−x−yAlyP

InxGa1−x−yAlyP, with y=0.0 to y=0.52, has been grown lattice matched to GaAs substrates using the technique of gas‐source molecular‐beam epitaxy. Growth conditions were established that resulted in conducting quaternary layers for both n‐type Si doped and p‐type Be doped samples. Si doped quaternary layers had a significantly reduced electron concentration at room temperature that varied with the AlP content in the InGaAlP layer. Intentionally doped InGaAlP layers exhibited room temperature photoluminescence for AlP mole fractions up to y=0.37; photoluminescence peak energies were 1.9 eV when y=0.0 (InGaP) to 2.3 eV when y=0.37 and decreased in intensity for increasing y.

Gas‐source molecular‐beam epitaxial growth of InGaAsP for 1.3 μm distributed Bragg reflectors

High‐quality InGaAsP films were grown on (100) InP substrates by gas‐source molecular‐beam epitaxy for use in distributed Bragg reflectors (DBR) operating at the wavelengths of 1.1–1.4 μm. By adjusting the inlet pressures of the feedstock gases AsH3 and PH3, precise control of the InGaAsP film composition was reproductively obtained, as evidenced by lattice mismatch of ≤ 5 × 10−4 and band‐gap wavelength variation of ≤10 nm. The InGaAsP films exhibited x‐ray diffraction peak widths as small as 21 arcsec and a low‐temperature photoluminescence peak width of 4.6 meV. Using 35.5 periods of alternating quarter wavelength layers of InGaAsP (1.15 μm composition) and InP, a DBR with a maximum reflectivity of 96±2% at the wavelength of 1.31 μm is demonstrated.

Strain-induced modifications of the band structure of In/sub x/Ga/sub 1-x/P-In/sub 0.5/Al/sub 0.5/P multiple quantum wells

The effect of strain on the band structure of In/sub x/Ga/sub 1-x/P-In/sub 0.5/Al/sub 0.5/P multiple quantum wells (MQWs) has been investigated from high-pressure and low-temperature photoluminescence measurements. The biaxial strain in the wells was varied between +0.6% compressive to -0.85% tensile strain by changing the well composition x from 0.57 to 0.37. Strain increases the valence band offsets in either tensile or compressively strained structures. Whereas relatively insensitive to tensile strain, the valence band offsets showed a strong dependence on the magnitude of the compressive strain. Good agreement is found between the measured valence band offsets and those predicted by the model solid theory, except for the largest compressively strained MQWs, for which the model calculations underestimate the measured valence band offset. Strain and the associated variations in composition also modified the separation among the well states associated with /spl Gamma//sub 1c/, L/sub 1c/, and X/sub 1c/. From these results, the bandgaps of each conduction band extrema were calculated in In/sub x/Ga/sub 1-x/P for 0.37

Reflection high‐energy electron diffraction patterns of CrSi2 films on (111) silicon

Highly oriented films of the semiconducting transition metal silicide, CrSi2, were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi_2(001)/Si(111). Reflection high‐energy electron diffraction (RHEED) yielded symmetric patterns of sharp streaks. The expected streak spacings for different incident RHEED beam directions were calculated from the reciprocal net of the CrSi_2(001) face and shown to match the observed spacings. The predominant azimuthal orientation of the films was thus determined to be CrSi_2〈210〉∥Si〈110〉. This highly desirable heteroepitaxial relationship may be described with a common unit mesh of 51 A^2 and a mismatch of −0.3%. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi_2〈110〉∥Si〈110〉. A new common unit mesh for this competing orientation is suggested; it possesses an area of 612 A^2 and a mismatch of −1.2%.