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Hydride vapor phase epitaxy grown n-GaN/sapphire (0001) was studied using Raman spectroscopy and high spatial resolution thermal conductivity.

A new study uses spectral elipsometry to investigate the complex dielectric interactions of two epitaxial layers of GaInAsSb/GaSb.

Research was conducted to examine three In(sub 1-x)Ga(sub x)As(sub y)P(sub 1-y)/InP p-i-n multiple quantum well laser structures with various p-doping profiles using contactless electroreflectance and piezoreflectance. The electric field and the amount of p-dopant interdiffusion were analyzed based on the observed Franz-Keldysh oscillations originating in the i-InGaAsP regions. The values of the quantities were in good agreement with high resolution x-ray diffraction calculations.

Four pseudomorphic AlGaAs/InGaAs/GaAs high electron mobility transistor structures with various quantum well compositional profiles were characterized by room-temperature photoreflectance (PR) and photoluminescence. Several features from the InGaAs modulation doped quantum well portion of the samples were seen in addition to signals from the AlGaAs, GaAs and GaAs/AlGaAs superlattice buffer layer. The PR spectra from the InGaAs quantum well channel can be explained by a line shape function which is the first derivative of a step-like two-dimensional density of states and a Fermi level filling factor.

A study was conducted to analyze the optical constants of a series of CdTe(sub 1-x)S(sub x) (0

A study was conducted to analyze six nominal In(sub 0.48)(Ga(sub 1-x)Al(sub x))(sub 0.52)P layers prepared on GaAs(001). The quaternary alloy was prepared by low pressure metalorganic chemical vapor deposition turbo disk technology. A combination on nondestructive methods was utilized to understanding the growth parameters of the alloy. These include high resolution x-ray diffraction, atomic force microscopy and reflectance anisotropy.

Electroreflectance (ER), piezoreflectance (PZR) and secondary ion mass spectrometry (SIMS) were employed to analyze two In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) solar cell structures with intrinsic (1)-InP spacers and two InP p-i-n samples. The composition, strain and well width of the MQWs were described by comparing the rich ER/PZR spectra from the MQW regions with an envelope function computation. From the electric fields coming from the i-InP region of the two InP p-i-n control samples, the amount of p-dopant interdiffusion was assessed based on the SIMS data. The results are discussed.

A study was conducted to characterize a pseudomorphic 0.98 micron meter InGaAs/GaAs/GaAlAs graded index of refraction separate confinement heterostructure (GRINSCH) laser utilizing contactless electroreflectance. Results showed that the operational temperature of the laser can be identified via the 11HH transition. A general expression for Franz-Keldysh oscillations in the presence of both electric fields were presented.

A study was conducted to investigate the origins of the Franz-Keldysh oscillations (FKO), observed in electromodulation and associated with the fields in the Ga(sub 1-x)Al(sub x)As emitter and GaAs collector regions of heterojunction bipolar transistor structures. Analytical expressions were determined for the origins of the FKOs. Results indicated that the FKOs from the collector characterize the maximum collector space charge field at the collector-base junction.

A study was conducted on the integer quantum Hall effect in a high electron density Al0.2Ga0.8As/In0.2Ga0.8As/GaAs quantum well. Results show a m=0.082m carrier effective mass. The transport relaxation time-quantum lifetime ratio suggests that long-range remote ion scattering was the dominant scattering mechanism. The results also reveal that the integer quantum Hall effect in the high electron density quantum well is similar to those of other systems.

The power of surface photovoltage spectroscopy in obtaining the performance parameters of actual laser devices was realized following an analysis of an InGaAs/GaAs/AlGaAs single quantum well graded-index-of-refraction separate-confinement hetero-structure laser. Conducted in a contactless way, surface photovoltage spectroscopy revealed the growth parameters of the single quantum well laser structure, such as the InGaAs well and cladding compositions, the InGaAs well width and other electro-optic structure data.

High spatial/depth resolution k measurements at 300 K of the Zn and O faces of two n-type ZnO (0001) samples fabricated by a vapor-phase technique is reported. A correlation between effective k values from the scanning thermal microscopy (SThM) scans and topography was established by simultaneously performing atomic force microscopy (AFM) scans.

Research describing the photoreflectance at 300k of a chirped superlattice heterojunction bipolar transistor structure is presented. The inbuilt dc electric fields and associated doping levels are investigated.

Contactless electroreflectance, in the range of 18

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter of A exciton deduced for the Ga (5×10[SUP5] dislocation cm[SUP-2] and N (1×10[SUP7] dislocation cm[SUP-2]) faces are 3 and 7 meV, respectively, indicating a lower defect concentration on the former face. The parameters that describe the temperature dependence of the interband transition energies of the A, B, and C excitons as well as the broadening function of the A and B features are evaluated. The results from an analysis of the temperature dependence of the broadening function of excitons A and B indicate that GaN exhibits a very large exciton-phonon coupling. [ABSTRACT FROM AUTHOR]

The optical constants ε(E)=ε[sub 1](E)+iε[sub 2](E) of unintentionally doped cubic GaN grown on GaAs(001) have been measured at 300 K using spectral ellipsometry in the range of 1.5-5.0 eV. The ε(E) spectra display a structure associated with the critical point at E[sub 0] (direct gap) and some contribution mainly coming from the E[sub 1] critical point. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden-Muñoz model dielectric function [M. Muñoz et al., J. Appl. Phys. 92, 5878 (2002)]. This model is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E[sub 0], E[sub 0] + Δ[sub 0] and the E[sub 1], E[sub 1]+Δ[sub 1], doublet. In addition to evaluating the energy of the E[sub 0] critical point, the binding energy (R[sub 1]) of the two-dimensional exciton related to the E[sub 1] critical point was estimated using the effective mass/k•p theory. The line shape of the imaginary part of the cubic-GaN dielectric function shows excitonic effects at room temperature not withstanding that the exciton was not resolved. [ABSTRACT FROM AUTHOR]

We have investigated a 1.3 µm InGaAlAs/InP vertical-cavity surface-emitting laser (VCSEL) structure using angle- and temperature-dependent wavelength-modulated differential surface photovoltage spectroscopy (DSPS). The DSPS measurements as functions of incident angle and temperature have been carried out in the ranges 0°≤θ≤60° and 300K≤T≤420K, respectively. Angle-dependent reflectance (R) and surface photovoltage spectroscopy (SPS) measurements have also been performed to illustrate the superior features of the DSPS technique. The differential surface photovoltage (DSPV) and SPV spectra exhibit both the fundamental conduction to heavy-hole excitonic transition of quantum well and cavity mode (CM) plus a rich interference pattern related to the mirror stacks, whereas in the R spectra only the CM and interference features are clearly visible. The energies of the excitonic transition and CM are accurately determined from the DSPV spectra. By changing the angle of incidence in the DSPS measurements the energy positions of the CM and distributed Bragg reflector features show a blueshift while the excitonic transition remains unchanged. At a fixed incident angle, the energy positions of the excitonic feature and CM show a different rate of redshift with increasing temperature, with the latter at a much slower pace. The results demonstrate considerable potential of DSPS for the nondestructive characterization of the VCSEL structures. [ABSTRACT FROM AUTHOR]

Using micro-Raman spectroscopy we have investigated the n dopant and strain distribution in lateral epitaxial overgrowth technique GaN films grown by metalorganic chemical vapor deposition on the sapphire (0001) substrates with SiN[sub x] masks. The widths of the mask stripes were 2, 4, 8, or 16 µm, while the mask windows were always 4 µm wide. In the case of narrow stripes (2 and 4 µm), when the overgrowth wings were well coalesced, the films were found to be fairly uniform with a background n doping of (4±2) × 10[sup 17] cm[sup -3]. The GaN wings in the samples with 8 and 12 µm stripes did not coalesce, leaving "V"-shaped and trapezoidal grooves, respectively. In the latter case, additional doping [ n = (6.5 ± 0.6) × 10[sup 17] cm[sup -3]] of the wing area was revealed, which may be due to surface diffusion of Si atoms from the SiN[sub x] mask to the GaN growth front and their incorporation into the growing film. [ABSTRACT FROM AUTHOR]

The optical constants ∊(E)=∊[SUB1](E)+i∊[SUB2](E) of unintentionally doped In[SUB0.53]Ga[SUB0.47]As lattice matched to InP have been measured at 300 K using spectral ellipsometry in the range of 0.4 to 5.1 eV. The ∊ (E) spectra displayed distinct structures associated with critical points at E[SUB0] (direct gap), spin-orbit split E[SUB0]+Δ[SUB0] component, spin-orbit split E[SUB1], E[SUB1]+ Δ, E[SUP ′,SUB 0] feature, as well as E[SUB2]. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden model dielectric function [Holden et al., Phys. Rev. B 56, 4037 (1997)], plus a Kramers-Kronig consistent correction, described in this work, that improves the fitting at low energies. This extended model is based on the electronic energy-band structure near these critical points plus excitonic and band-to-band Coulomb-enhancement effects at E[SUB0], E[SUB0]+ Δ[SUB0], and the E[SUB1], E[SUB1] + Δ[SUB1], doublet. In addition to evaluating the energies of these various band-to-band critical points, information about the binding energy (R[SUB1]) of the two-dimensional exciton related to the E[SUB1], E[SUB1] +Δ[SUB1] critical points was obtained. The value of R[SUB1] was in good agreement with effective mass/k·p theory. The ability to evaluate R[SUB1] has important ramifications for first-principles band-structure calculations that include exciton effects at E[SUB0], E[SUB1], and E[SUB2] [M. Rohlfing and S. G. Louie, Phys. Rev. Lett. 81, 2312 (1998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)]. [ABSTRACT FROM AUTHOR]

An angle-dependent wavelength-modulated differential-photovoltage spectroscopy (DPVS) investigation has been performed at room temperature on a bare as-grown wafer of GaAs/ GaAlAs-based vertical-cavity surface-emitting laser (VCSEL) structure, designed for emitting at a wavelength near 850 nm. The differential-photovoltage (DPV) spectra exhibit both the fundamental conduction to heavy-hole excitonic transition and cavity mode plus an interference pattern related to the mirror stacks. By changing the angle of incidence in the DPV measurements the energy positions of the cavity mode and distributed Bragg reflector features show a blueshift while the excitonic transition remains unchanged. The energies of the excitonic transition and cavity mode are accurately determined from the DPV spectra. The advantages of DPVS in relation to other methods of characterizing VCSEL structures, such as surface photovoltage, photoreflectance, photocurrent, and differential photocurrent spectroscopy, are discussed. The results demonstrate considerable potential of DPVS for the nondestructive characterization of these structures at room temperature. [ABSTRACT FROM AUTHOR]

We report details of the calculation of the lattice thermal conductivity κ in wurtzite GaN. Numerical simulations are performed for n-type wurtzite GaN with different density of silicon dopants, point defects and threading dislocations. Using the material specific model we verified the experimentally observed linear decrease of the room-temperature thermal conductivity with the logarithm of the carrier density n. The decrease was attributed mostly to the increased phonon relaxation on dopants. Our calculations show that the increase in the doping density from 10[sub 17] to 1018 cm[sub -3] leads to about a factor of 2 decrease in thermal conductivity from 1.77 W/cm K to 0.86 W/cm K. We have also established that the room-temperature thermal conductivity in GaN can be limited by dislocations when their density is high, e.g., N[sub D] > 10[sup 10] cm[sup -2]. The obtained results are in good agreement with experimental data. The developed calculation procedure can be used for accurate simulation of self-heating effects in GaN-based devices. [ABSTRACT FROM AUTHOR]