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The forward voltage drop (Vf) increase observed in 4H-SiC bipolar devices such as pin diodes due to recombination-induced Shockley stacking fault (SSF) creation and expansion has been widely discussed in the literature. It was long believed that the deleterious affect of these defects was limited to bipolar devices. However, it was recently reported that forward biasing of the body diode of a 10kV 4H-SiC DMOSFET led to similar Vf increases in the body diode I-V curve as well as a corresponding degradation in the majority carrier conduction characteristics as well and this degradation was believed to be due to the creation and expansion of SSFs during the body diode forward biasing. Here we report measurements comparing the influence of similar stressing, along with annealing and current-induced recovery experiments in DMOSFETs and merged pin-Schottky diodes with the previously reported results of these experiments in 4H-SiC pin diodes. The results of these experiments provide sufficient support that the observed degradation in the majority carrier conduction characteristics is the result of SSF expansion.

Here we present optical beam induced current, electroluminescence, time resolved photoluminescence and current-voltage measurements on several 4H-SiC PiN diodes containing in-grown stacking faults (IGSFs). These defects were observed to act as either current shorts, creating a direct electrical contact between the p+ and n+ layers, or as a current barrier. Carrier lifetime measurements verify that the change in behavior is indeed associated with changes in the conductivity of the material in the vicinity of the defect and not due to local changes in the carrier lifetime. The IGSFs discussed here appear to differ from those previously discussed in the literature and may constitute a new, multi-layered IGSF.

Optical Impedence Spectroscopy of GaN/AlGaN high electron mobility transistor structures (HEMTs) using photoreflectance exhibit a photoreflectance lags – the component of the modulated reflectance out of phase with the chopper – ranging from 0.1 to 0.5. Photoreflectance was performed using below gap pumping on various samples. Samples that do exhibit appreciable photoreflectance lag for above gap pumping show significantly enhanced photoreflectance signals for below gap pumping. Yet, samples that do not exhibit appreciable photoreflectance lag for above gap pumping do not exhibit a signal for below gap pumping. This implies that the photoreflectance phase lag is due to mid-gap trap states. At least 2 types of traps are found, above and below about 2.5 eV. This result means that that photoreflectance can be used as a probe of HEMT device quality.

Photoreflectance (PR) is used to detect and characterize the electronic effects etch-induced defects in GaN that is exposed to an Ar or Ar/Cl inductively coupled plasma (ICP). Because of the sensitivity of PR we can follow the formation of etch-induced defects as a function of ion energies and densities. We show that at low RF powers, below 100W, the surface improves in electronic quality, but as the power is increased beyond 200W, etch-induced defects, are formed. The use of an Ar/Cl mixture plays a critical role in control of etch-induced defects.

Reflectance difference anisotropy (RDA) and low energy electron diffraction (LEED)have been used to study the formation of Ga or Al chains and nanowires on the Si(112) surface. At T > 350°C, the Ga or Al chains form at the step edges by a self-limiting process, while at lower temperatures, Ga or Al nanowires form on the terraces in addition to the chains on the ledges. The process has been tracked in real time from the rapid change of the (2×1) Si(112) reconstruction under subcritical coverage to chain formation leading to a 5×1 reconstruction followed by a 6×1 reconstruction’. During sequential deposition of Ga and Al, we observe (in RDA and AES) that Ga atoms forming the chains can be replaced by Al, indicating a stronger Al-Si bond strength and confirming the chemical sensitivity of the light scattering in RDA. Low temperature depositions (in the 300’C range) are shown to lead to the formation of Al (or Ga) metallic wires on the Si(111) terraces. Continued deposition of less than 10 monolayers at T below 250°C leads to a very anisotropic but patterned Al or Ga structure in registry with the substrate which retains an unexpectedly large polarizability for coverages as thick as 40 ml.

We experimentally demonstrate the annealing and electrical activation of doped silicon without the direct application of heat as in conventional thermal annealing or pulsed laser annealing. 25 × 25 × 3 mm samples of silicon doped by neutron transmutation were irradiated with a short pulse from a 1.06-micron laser. The few joule laser pulse was focused to mm-diameter surface spot which resulted in high power (∼ 1011W/cm2) capable of launching shocks into the entire sample. In a few instances the entire silicon slab, including regionsfar outside the illuminated spot, was annealed and electrically activated. In the annealed samples electrical activation of donors throughout the slab, measured with a four-point probe, was uniform and comparable to that of thermally annealed control samples. Far-infrared spectroscopy and Hall measurements also showed that the donor species was activated and Raman spectroscopy demonstrated marked improvement in the crystal structure. We conjecture that the annealing was caused by the mechanical energy that was launched into the slab by the laser pulse. Results of experiments on an ion-implanted silicon sample are also discussed.

The growth and energetics of Ga chains on a Si(112) facet surface have been investigated. Low energy electron diffraction (LEED) and Reflectance Difference Anisotropy (RDA) experiments have been performed in UHV to examine the kinetics of the Ga atom chain formation process along the Si steps. This is a self-limiting process for substrate temperatures in the 400°C to 500°C range, since the binding energy of the metal atoms at the step edges is greater than that on the (11l)-type terraces. At saturation coverage, the Ga chains exhibit sixfold periodicity along the step edges, but below saturation, these chains exhibit fivefold periodicity. A model has been suggested from these results in which the periodicities of the chains are determined by the metal atom vacancies, which balance the tensile stress created by the larger metal atoms. We have used RDA to study the time evolution of the surface kinetics and changes in the surface reconstruction of Ga deposited on these facet (112) Si surfaces, as a function of substrate temperature and Ga deposition rate. The RDA measurement is shown to be sensitive to the formation of both the 5×1 as well as 6 × 1 reconstructions and to island formation at low substrate temperatures. The diffusion-controlled Ga line formation process at low temperatures has also been characterized as well as the evaporation controlled regime, which is evident at substrate temperatures over 400°C.

High density plasma etching of Hg1−xCdxTe in CH4/H2/Ar chemistry is examined using mass spectroscopy with careful surface temperature monitoring. The dominant etch products are monitored as a function of surface temperature (15–200°C), ion energy (20–200 eV), total pressure (0.5–5 mTorr), microwave power (200–400 W), and flow fraction of methane in the etch gas mixture (0–30%). In addition, observations are made regarding the regions of parameter space which are best suited to anisotropie, low damage etch processing. These observations are compared with previous results in the form of scanning electron micrographs of etched features for anisotropy evaluation and Hall effect measurements for residual damage. Insights to the overall etch mechanism are given.

High density plasma etching of III-V compound semiconductors is critically important to the development of advanced optoelectronic and high frequency devices. Unfortunately, the surface chemistry of these processes is not well understood. In an effort to monitor surface processes and their dependence on process conditions in a realistic etching environment, we have applied mass spectroscopic techniques for the study of GaAs etching in Cl2/Ar chemistry. Etch product chlorides were monitored, together with optical measurement of the surface temperature by diffuse reflectance spectroscopy, as pressure (neutral flux), microwave power (ion flux) and rf bias of the substrate (ion energy) were varied. Observations from the spectroscopic techniques were correlated with ex situ surface damage assessments of unpassivated surfaces by photoreflectance spectroscopy. As a result, insights are made into regions of process conditions that are well suited to anisotropic, low damage etching.

Discrete Fourier transform (DFr) techniques have been applied to the analysis of the Franz-Keldysh oscillations used in determining electric fields. It is shown that the DFT can be applied to a wide range of EM line shapes and that it can yield accurate results for the electric fields in the case where one field is present in the sample. For cases where there are contributions to the EM spectrum from either two electric fields or two degenerate transitions, such as excitations originating from light- and heavy-hole valence bands, care must be applied in extracting the field from the lower intensity DF” peak. The window used to obtain the DFT influences the peak position of lower intensity DFT peak and thus can lead to spurious shifts of the line.

The effects of P2S5 surface passivation treatments on damage caused by chemically assisted ion beam (CAIBE) etching of GaAs have been examined using ex-situ photoreflectance. Epitaxially grown undoped GaAs on heavily doped GaAs substrates were used to determine surface electric fields. The etching process is observed to decrease surface electric fields, produce subsurface damage and to reduce surface photovoltages. Post-etching treatments with P2S5 are observed to increase surface photovoltages, but have no significant effect on the surface fields or subsurface damage. That the surface field is unaffected suggests that in etched materials the Fermi level pinning is not solely determined by the surface and that the near surface regions are important. We also find that samples pretreated with P2S5 exhibit more etch damage than those which are only degreased.

Porous silicon layers have been formed which exhibit photoluminescence (PL) peaks that do not blueshift with increasing porosity. Hydrogen desorption experiments have been performed in vacuum under anneals between 230°C–390°C. Simultaneous, in-situ PL measurements show that the PL intensity decreases and disappears with decreasing hydrogen content. Infrared spectroscopy (IR) measurements also show loss of hydride species in the same temperature range. These results indicate that hydrogen is important in the PL process. We suggest that silicon hydrides are the source of PL in porous SI.

Chemically assisted ion beam etching (CAIBE) of Si1−Gex films is reported. Ar+ ion sputtering in the presence of Cl2 background gas has been used to etch epitaxial films of Si1−xGex, with x ranging between 0 and 0.5. It is found that Si1−xGex, sputters more rapidly than Si, but less than Ge. The use of C12 gas enhances the sputter rates of SiGe as in the case of Si. Analysis of the etch rates indicates that the etch rate increase is due to an enhancement of the sputtering process, rather than a chemical effect.

Oxide layers that are thick (>200 Å and uniform have been produced on GaAs (110) and (100) by reacting the substrate (Ts2O3 and As2O5 or GaAsO4. Raman spectroscopy indicates that there is no metallic (amorphous or crystalline) As in the oxide or at the interface between the oxide and substrate and that there is no appreciable oxidation induced disorder of the substrate as is seen in high temperature thermal oxidation processes.

Modulation spectroscopies, such as electroreflectance and photoreflectance have become popular as room temperature probes of layered structures. Because of their derivative nature, one observes sharp optical features related to critical points in the dielectric function of the material under study. This allows us to obtain information such as alloy concentration, carrier density, well widths of quantum wells and thicknesses of the constituent layers in superlattices. In this paper, we will review the application of modulation spectroscopy to the study of optical and electronic properties of layered structures.