S. Mo

Characterization of surface damage in dry-etched InP

Sn-doped InP wafers were etched by reactive ion beam etching (RIBE) using a gas mixture of at ion energies varying from 100 to 600 eV. We investigated the radiation damage caused by RIBE using various techniques which are sensitive to the near-surface region. The optical and electrical properties of the damaged layer as a function of ion energy were studied by photoluminescence microscopy (PLM), photoluminescence spectroscopy, spectroscopic ellipsometry (SE) and electrochemical capacitance - voltage profiling. The electron channelling pattern technique (ECP) was used to examine the structural disorder. The observed radiation damage was attributed to the formation of phosphorus vacancies indicating preferential loss of phosphorus in the InP. We found optimum etching conditions at an ion energy of 400 eV representing the best trade-off between high etch rate and low radiation damage. The potential of PLM, SE and ECP as fast and non-destructive techniques for quality control in research as well as manufacturing is demonstrated.

High-quality In0.53Ga0.47As on exactly (001)-oriented Si grown by metal-organic vapour-phase epitaxy

Abstract In this paper we report on results of an optimized growth process of In0.53Ga0.47As on exactly (001)-oriented Si substrates by low-pressure metal-organic vapour-phase epitaxy (LP-MOVPE). The crystalline perfection of the InGaAs as well as an intermediate layer sequence consisting of GaAs, InP and an InGaAs InP superlattice was examined by transmission electron microscopy, X-ray diffractometry, and dislocation etching. Electrical and optical characterization were performed using electrochemical capacitance-voltage profiling and photoluminescence spectroscopy. The InGaAs layer exhibits a lattice mismatch of 1 × 10−3 to InP, an etch-pit density of 1.3 × 108 cm−2, full widths at half maximum of 210 arcsec of the (004) X-ray reflex and of 15 meV of the excitonic photoluminescence peak at 2 K as well as a background doping concentration of 4 × 1016 cm−3. Using this layer high-performance photodetectors for the long-wavelength range were fabricated.

Photoreflectance Study on the Effect of Lattice Defects in InP on (001) Si

The residual stress in epitaxial InP on (001) Si was investigated by photoreflectance spectroscopy. Depending on doping concentration, low-field and intermediate-field spectra were measured which were quantitatively analysed by a third-derivative approximation or by a multilayer model, respectively. In both cases, transitions only from the heavy-hole and the split-off valence subbands into the conduction band contributed to the spectra, while the light-hole to conduction-band transition was absent. In addition to the energy shift due to tensile strain caused by the different thermal expansion coefficients of InP and Si, a signal component originating from compressive strain in the InP was observed. This effect is attributed to the clustering of dislocations at twin defects. As a result, a model of the defect distribution in the heteroepitaxial InP layers was presented.

Temperature dependence of residual stress in epitaxial GaAs/Si(100) films determined from photoreflectance spectroscopy data

In the temperature range T=10–300 K, photoreflectance spectroscopy was used to study the temperature dependence of residual stress in epitaxial n-GaAs films (1–5 µm thick, electron concentration of 1016–1017 cm−3) grown on Si(100) substrates. A qualitative analysis showed that the photoreflectance spectra measured in the energy region of the E0 transition in GaAs had two components. They consisted of the electromodulation component caused by the valence subband |3/2; ±1/2〉-conduction band transition and the low-energy excitonic component. The magnitude of stress was determined from the value of the strain-induced energy shift of the fundamental transition from the subband |3/2; ±1/2〉 with respect to the band gap of the unstressed material E0(T)-E0|3/2; ±1/2〉(T). The increase in the energy shift E0-E0|3/2; ±1/2〉 from 22 ± 3 meV at 296 K to 29 ± 3 meV at 10 K, which was found in the experiments, gives evidence of an increase in biaxial stress with decreasing temperature.

Characterization of thin buffer layers for strongly mismatched heteroepitaxy

Thin buffer layers for strongly mismatched heteroepitaxy of GaAs and InP on Si were investigated with respect to their structural characteristics in a scanning electron microscope (SEM). A novel technique, which is based on energy-dispersive X-ray spectrometry (EDX), was utilized for thickness measurement. With GaAs thicknesses were determined in the range from several μm down to 10 nm. Their accuracy was confirmed by mechanical surface tracing of selectively etched steps. The crystal quality of the thin layers was probed by electron-channelling patterns (ECP). We found a dependence on buffer-layer thicknesses which was confirmed by spectroscopic ellipsometry. For thin layers the optical absorption coefficient near the band edge, which is a measure of the density of structural defects in thin layers, showed the smallest deviation from the bulk standard. Furthermore, the buffer-layer quality determined by ECP was correlated with the surface morphology and with the density of twin defects in subsequently grown thick main layers of GaAs and InP, respectively. We conclude that EDX and ECP are powerful methods for the structural characterization of thin buffer layers playing a key role in mismatched heteroepitaxy. Both techniques were performed in a SEM, which is a standard tool in research and development as well as in industrial laboratories.

Selected-area electron-channeling pattern as a characterization method for heteroepitaxial layers

Strongly mismatched III/V-compound semiconductor heteroepitaxial layers on Si were investigated with respect to their crystal quality by quantitative analysis of selected-area electron-channeling patterns (SAECP). An algorithm, based on the statistical analysis of 2-D SAECPs using digital image processing, is described. Agreement is found between the crystal quality of the thin nucleation layers obtained by SAECP and the density of structural defects as determined by spectroscopic ellipsometry. Furthermore, an area-selectively thinned InP/Si sample was examined by SAECP to obtain the dislocation density versus the residual layer thickness. The dislocation-density distribution agrees well with the theoretical prediction and experimental reference data.

Strain-induced photoreflectance spectra in the vicinity of the E0 transition in GaAs/Si and InP/Si heterostructures

A study is reported of the structure of photoreflectance (PR) spectra in the vicinity of the E0 transition from thin (d=1–5 µm) n-GaAs and n-InP films (n=1016–1017 cm−3) grown epitaxially on Si(001) substrates. A quantitative analysis of the spectra involving multi-component fitting shows that the electronic optical transition from the {3/2;±1/2} subband provides a dominant contribution to the intermediate-field electromodulation component in both systems. The splitting observed in the GaAS/Si PR spectra near the main peak are accounted for not by the strain-induced valence-band splitting but rather by a spectral superposition of the intermediate-field component due to the {3/2;±1/2} subband with a low-energy excitonic component. The analytically established transition energy E03/2;±1/2 is used to calculate biaxial strains in epitaxial films.

Vibration sensor with optoelectronic interface

A micromachined sensor for wear monitoring of rotating machinery is described. It comprises a Si microelectromechanical transducer for vibration sensing, on-chip MOS circuitry for amplification and a hybrid GaAs/GaAlAs infrared emitting diode (IRED) for electrooptical conversion of the measured signal. Bulk micromachining combined with common MOS technology is used for transducer fabrication. In view of a monolithic integration of an IRED heteroepitaxy on Si was investigated.