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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]

We have measured high spatial/depth resolution (2–3 μm) thermal conductivity (κ) at 300 K before and after plasma-induced effects on two series of n-GaN sapphire (0001) samples fabricated by hydride vapor phase epitaxy using scanning thermal microscopy. The sample thicknesses were 50±5 μm for one set and 25±5 μm for the second. The carrier concentrations were ∼8×10[sup 16] cm[sup -3] and ∼1.5×10[sup 17] cm[sup -3], respectively, as determined by Hall effect measurements. The thermal conductivity before treatment was similar to that previously reported for hydride vapor phase epitaxy material with comparable carrier concentration and thickness [D. I. Florescu et al., J. Appl. Phys. 88, 3295 (2000)]. Damage was induced by ion-beam processing the samples under constant Ar[sup +] gas flow and pressure for a fixed period of time (5 min), with the dc bias voltage (V[sub dc]) being the only variable processing parameter (125–500 V). The thermal conductivity near the surface, κ, was found to exhibit a linear decrease with V[sub dc] in the investigated range after this procedure. A second process was then applied in order to remove some damage. In this case the samples were processed under a constant mixture of Cl[sub 2] and Ar[sup +] gas flow and V[sub dc][sup ′] of 50 V. For the samples with V[sub dc] in the range 125 V

Temperature-dependent contactless electroreflectance (CER) and photoluminescence (PL) measurements in the range of 30 K

Measures the high resolution thermal conductivity and Raman spectra of hydride vapor phase epitaxy grown n-GaN/sapphire. Thermal conductivity; Raman spectroscopy; Improvement of thermal conductivity with the increase in film thickness.

Presents information on a study which determined the optical properties of cadmium telluride polycrystalline thin-films. Experimental details; Results and discussion.

Presents a study which investigated the temperature dependence of the E[sub1] optical feature of Hg[0.65]Cd[0.35]Te using electroreflectance in the metal insulator semiconductor configuration. Properties of the narrow-gap semiconductor Hg[sub1-x]Cd[subx]Te; Materials and methods used; Description of the experimental electroreflectance spectra in the E[sub1] spectral region; Plot of the temperature dependence of the E[sub1] transition energy.

Investigates photoreflectance, electrolyte photoreflectance (PR) and electrolyte electroreflectance (EER) for various reactive ion etching treatments of n-silicon. Use of modulation spectroscopy; Dependence of the amplitude of the EER transition on the electrode potential for untreated silicon; Low-field limit of EER and PR.

Presents results of a systematic and extensive investigation of polish-induced surface strain in gallium arsenide an indium phosphide using Raman scattering. Experimental details; Use of argon-ion laser as an excitation source in measurements; Conclusion of the study.

Focuses on a study conducted using the contactless electroreflectance for the characterization of the complete profile of the pseudomorphic0.98 ...m InGaAs/GaAs/GaAlAs graded index of refraction separate confinement heterostructure (GRINSCH) laser. Importance of the nondestructive characterization and qualification of complex semiconductor multilayer structures; Reference to the fabrication process; Description of the modulation methods.

Provides information on a study deriving expression for the origins of the Franz-Keldysh oscillations (FKOs) observed in the electromodulation spectra of graded emitter Ga1-xAlxAs/GaAs heterojunction bipolar transistor structures. Information on the graded emitter-based region; Detailed information on the model structure; Indepth look at the numerical calculation and comparison with experiment.

Presents a study which investigated the integer quantum Hall effect (IQHE) in a low temperature magne-totransport of an A10.2Ga0.8As/In0.2Ga0.8As/GaAs quantum well (QW) structure to determine the basic device parameters. Experimental procedure use; Determination of pre-exponential factors; Results and discussion on the study.

Presents a study on surface photovoltage spectroscopy of an InGaAs/GaAs/AIGAAs single quantum well laser structure determined by numerical simulation. Discussion on the study conducted on SPV spectra of the GRINSCH laser; Information on the dependence of SPV onset energy; Results obtained from the study.

Discusses the characterization of ZnCdMgSe epitaxial layers grown on indium phosphide substrates. Measurements of etch pit density; Characterization of the morphology of the etched surface using atomic force microscopy; Accuracy of the etch pit density method for revealing stacking faults and dislocations.

We have modified the properties of diamondlike atomic-scale composite (DLASC) material of various thicknesses (5-70 μm) by means of cw Ar−ion laser annealing using a focused beam (∼ 2 μm spot size). These DLASC films [amorphous “diamondlike/quartzlike” a-(C:H/Si:O)] constitute a novel class of diamond-related materials. The laser annealing effects were investigated by micro-Raman scattering. The structure of these films can be altered locally from amorphous to nanocrystalline depending not only on the parameters of the annealing process (annealing time, laser intensity) but also the mechanical properties (hardness, stress) of the films. For comparison purposes we also measured the effects of thermal annealing. [ABSTRACT FROM AUTHOR]

Presents information on a study which assessed the piezoreflectance and photoreflectance of gallium digital alloy structures. Methodology of the study; Results and discussion; Conclusion.

Presents information on the measurement of the photoreflectance spectra of a strained layer (001) In[sub0.21]Ga[sub0.79]As/gallium arsenide single quantum well (SQW). Preparation of the SQW; Line shape considerations.

Presents a study which utilized electroreflectance spectroscopy to investigate a GaAs/Ga[sub0.77]Al[sub0.23]As coupled double quantum well (CDQW) system as a function of externally applied electric field. Detection of intra- and inter-well exciton transitions; Lineshape consideration for modulated reflectivity; Effects of electric fields on CDQW.

We have investigated a 1.3 μm InGaAlAs/InP (001) vertical-cavity surface-emitting laser (VCSEL) structure using surface photovoltage spectroscopy (SPS) and normal-incidence reflectivity. The SPS measurements were performed as a function of angle of incidence relative to the normal (0°–55°) and temperature (300 K

We measured high spatial/depth resolution 300 K thermal conductivity K of the Zn and O surfaces of two bulk n-type ZnO (0001) samples, grown by a vapor-phase transport method, using scanning thermal microscopy (SThM). The thermal investigation was performed in both point-by-point (∼2 μm resolution) and area-scan modes. On the first sample κ=1.16±0.08 (Zn face)/1.10±0.09 (O face) W/cmK while for the second material κ=1.02±0.07 (Zn face)/0.98±0.08 (O face) W/cmK. These are the highest K values reported on ZnO. A correlation between SThM area-scan readings and surface topography was established by simultaneously performing atomic force microscopy scans. The influence of surface roughness on the effective thermal conductivity (i.e., heat flow) is discussed. [ABSTRACT FROM AUTHOR]

We have measured the photoreflectance spectrum at 300 K from an AlInAs/GaInAs (lattice matched to InP) heterojunction bipolar transistor structure with a chirped superlattice (ChSl) grown by molecular-beam epitaxy. From the observed Franz-Keldysh oscillations we have evaluated the built-in dc electric fields and associated doping levels in the n-GaInAs collector and n-AlInAs emitter regions. The oscillatory signal originating from the ChSl is caused both by the uniform quasielectric and nonuniform space-charge fields in this region. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a comparative study of polish-induced effects in (100) gallium arsenide by Raman spectroscopy and cross-sectional electron microscopy. Similarities of depth dependence of the dislocation density and polish-induced strain; Information on the polish-time behavior of both types of polish-induced effects; Difference of skin depth evaluated by Raman scattering and transmission electron microscopy.