Showing papers by "Hongen Shen published in 1991"
TL;DR: In this paper, the time constants involved in photoreflectance from several GaAs surface-intrinsic n+ structures were determined from digital oscilloscope traces, and the dependence of rise and fall times on intensity and wavelength of pump and probe beams can be accounted for by a theory based on majority carrier flow.
Abstract: We have studied the time constants involved in photoreflectance from several GaAs surface‐intrinsic‐n+ structures. The rise and fall times were determined from digital oscilloscope traces. We find that they depend on the intensity and wavelength of the pump and probe beams. The observed photoreflectance feature does not always follow a single exponential decay. The dependence of rise and fall times on intensity and wavelength of pump and probe beams can be accounted for by a theory based on majority‐carrier flow. The characteristic time obtained can be used to determine the potential barrier height.
43 citations
TL;DR: Raman spectra from electrochemically etched porous silicon are correlated with photoluminescence (PL) data from the same spots of the sample, consistent with optical properties of quantum confinement as mentioned in this paper.
Abstract: Raman spectra from electrochemically etched porous silicon are correlated with photoluminescence (PL) data from the same spots of the sample. This correlation is consistent with optical properties of quantum confinement. The dielectric constant determined from angle resolved ellipsometry gives values far below that of bulk silicon. This reduction is due to the combined effects of voids as well as quantum confinement. The PL spectrum shows a weak high energy peak around 2.8eV in addition to the strong broad peak at 1.5 to 1.9eV. The temperature dependence of PL resembles that of bound excitons such as Si:S, having a thermal dissociation energy of 100 meV near room temperature. The radiation life time changes from tens of microseconds near room temperature to a few milliseconds at liquid helium temperatures. The rapid increase in lifetime and decrease in PL intensity at low temperatures indicates that phonons are probably involved.
17 citations
TL;DR: In this article, the authors determine the composition of InGaAsP films through measurements of the lattice spacings and band-gap energies (Eg) using an iterative procedure, using doublecrystal x-ray data with room-temperature photoreflectance results.
Abstract: Determining the composition of strained InGaAsP films through measurements of the lattice spacings and band‐gap energies (Eg) requires converting the measured values to ones which would correspond to unstrained material. In strained layers the lattice constants perpendicular and parallel to the growth plane can vary significantly from the relaxed value, and the optically measured Eg is affected by a strain‐induced splitting of the valence band and a shifting of the direct gap energy. By combining double‐crystal x‐ray data with room‐temperature photoreflectance results, we determine the InGaAsP composition accurately using an iterative procedure. Film compositions calculated using strain adjusted values of Eg agree with those determined by energy dispersive spectroscopy to within 1–2 at. %, whereas if energy shifts are not considered, the error approaches 10 at. % for strain on the order of 0.4%.
15 citations
05 Aug 1991
TL;DR: In this article, the contribution of surface and bulk recombination in GaAs:C samples was investigated using photoluminescence (PL) techniques, and the experimental results suggest that submicron AlGaAs/GaAs HBTs are suitable for ultra-high-speed IC applications.
Abstract: The device fabrication, high-frequency performance, and effects of a heavily-carbon-doped base on submicrometer AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are discussed. Photoluminescence (PL) techniques were employed to study the contributions of surface and bulk recombination in GaAs:C samples. PL intensity was quenched mainly by the bulk recombination mechanism in heavily-carbon-doped samples. The contribution from surface recombination is negligible. The emitter size effect is eliminated by using a single p/sup +/ (1*10/sup 20/ cm/sup -3/) base layer in the HBT structure. Use of a heavily-carbon-doped base layer provides for low base resistance while maintaining the abrupt acceptor profile required for high emitter injection efficiency. A maximum frequency of oscillation (f/sub MAX/) of over 100 GHz has been obtained from a submicron HBT (0.6 mu m*8.5 mu m). As a result of minimizing surface recombination in the extrinsic base region, f/sub MAX/ increases from 70 GHz to 91 GHz as emitter width decreases from 3.0 mu m to 0.6 mu m (*4.5 mu m) while f/sub T/ remains nearly unchanged. The experimental results suggest that submicron AlGaAs/GaAs HBTs are suitable for ultra-high-speed IC applications. >
3 citations