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Presents a reply to the commentaries of authors Aleksandra Djurisic and E. Herbert Li on the article by K. Wei et al. regarding the optical properties of cadmium telluride films. Failure of a number of schemes to model optical constants of diamond- and zincblende-type semiconductors; Deficiencies of Adachi model; Important parameters associated with Holden model.

We report a new type of normalization procedure for modulation spectroscopy experiments in order to obtain the relative change in the reflectance (transmittance) spectrum ΔR/R(ΔT/T). Our new technique utilizes a servomechanism driven variable neutral density filter which keeps the dc component of the signal from the detector constant by varying the intensity of the light striking the sample. This method is particularly useful for photoreflectance measurements which can have background problems due to scattered pump light and/or photoluminescence. Advantages for other modulation spectroscopies, particularly in the region of the fundamental band gap of semiconductors, also will be discussed. [ABSTRACT FROM AUTHOR]

Comments on the article 'Photoreflectance study in the E[sub 1] and E[sub 1] + delta[sub 1] transition regions of CdTe,' which appeared in the 'Journal of Applied Physics.' Optical transitions in diamond and zincblende semiconductors; Critical point energies.

Electroreflectance from Hg1-xCdxTe in the metal-insulator-semiconductor configuration at 77 K as a function of gate voltage has been investigated. We find the spectra consist of contributions from two considerably different compositions, one of which corresponds to semimetallic material (x≊0.1). The x≊0.1 component is a consequence of the passivation of the HgCdTe surface. There is some evidence that these two regions are distributed across the surface rather than in depth. In addition, the two components have different responses to the gate voltage. The higher composition region can be driven through a flat band while the lower composition portion cannot. [ABSTRACT FROM AUTHOR]

We have used Raman scattering as a nondestructive, contactless method for determining not only the free-carrier concentration N but also the width of the space-charge layer in <100> n-GaAs with 4×1017 cm-3≤N≤1×1019 cm-3 using as an excitation several different wavelengths of an Ar+ laser. By comparing the intensity at different wavelengths of the uncoupled longitudinal optic phonon mode originating in the space-charge layer with the signal from a piece of undoped <100> material, it is possible to experimentally evaluate the width of the depletion layer Ls. We find that there is very good agreement between the experimental values and those obtained from a generalized theory for both degenerate and nondegenerate materials. Thus, these experimental results demonstrate that for <100> III-V semiconductors, Raman scattering can be used as a contactless method to determine the width of the space-charge region for carrier concentrations up to 1×1019 cm-3. [ABSTRACT FROM AUTHOR]

We have studied Raman scattering from CdTe <100>, <110>, and <111> surfaces subjected to various surface treatments. Our investigation shows that 0.1% Br/methanol etch or chemomechanical polish leaves a thin residual layer of polycrystalline Te of thickness 10-40 Å (under a tensile stress of about 8 kbar) and that this Te film can be removed by a rinse in a 1 N KOH in methanol solution. [ABSTRACT FROM AUTHOR]

We report measurements of the first-order Raman spectra of the longitudinal optic phonon from <100> surfaces of GaAs and InP which have been polished by various procedures. Nondestructive depth profiling was accomplished by using the various excitation lines of an Ar+ laser. The resultant line shape changes have been quantitatively accounted for by a model based on the convolution of the penetration depth of the light and the skin depth of the polish-induced surface strain. We find the polish-induced surface strain to be compressive and about 4% in GaAs and 5% in InP, relatively independent of particle size. The strain skin depth is substantially less than the particle size although it does increase with increasing size and polishing time. [ABSTRACT FROM AUTHOR]

We have studied the photoreflectance spectra at 300 K from a number of GaAs/Ga1-x AlxAs heterojunction bipolar transistor (HBT) structures grown by molecular beam epitaxy and metalorganic chemical vapor deposition. From the observed Franz–Keldysh oscillations we have been able to evaluate the built-in dc electric fields Fdc in the Ga1-x Alx As emitter as well as the n--GaAs collector region. In addition, the Ga1-x Alx As band gap (and hence Al composition) has been determined. The obtained values of Fdc are in good agreement with numerically computed values for the analyzed HBT structures, thus making it possible to deduce doping levels in these sections. [ABSTRACT FROM AUTHOR]

Examines the characteristics of GaAs/Ga[sub 0.7]Al[sub 0.3]As quantum dots fabricated by reactive-ion etching. Analysis of the magnitude and nature of the process-induced strain in the dots; Transition between the conduction and valence bands; Details of photoreflectance features of the quantum dots.

Using photoreflectance at room temperature we have evaluated the topographical variations in quantum level transitions of a GaAs/GaAlAs multiple quantum well (220 Å/150 Å) due to changes in barrier height and quantum well width. The spatial resolution of the measurement was about 100 μm. A key feature of our analysis is the ability to fit the electromodulation spectra by a third-derivative functional form line shape factor. We can detect barrier height changes of several millielectron volts and variations in well width as small as 2 Å. [ABSTRACT FROM AUTHOR]

The photoreflectance (PR) spectra of several GaAs/AlAs superlattices have been measured at 300 and 77 K using monochromatic light sources (laser or monochromator) as a secondary (pump) beam, thus enabling us to study the wavelength dependence of the PR. We demonstrate for the first time that electromodulation spectra from superlattices can be fit by a third derivative functional line shape, thus making it possible to precisely determine energies, broadening parameters, amplitudes, and phases of the spectral features. This result greatly enhances the usefulness of electromodulation to study and characterize these structures. The wavelength dependence of the PR shows that there is more than one PR mechanism in superlattices, in contrast to bulk material. [ABSTRACT FROM AUTHOR]

We report a modulation spectroscopy experiment on GaAs and Ga0.82Al0.18As at elevated temperatures. Using the contactless electromodulation method of photoreflectance, the direct gaps (E0) of these materials have been observed from 77 K to 600 °C. The latter temperature is comparable to molecular beam expitaxy, metalorganic chemical vapor deposition, growth temperatures, etc. Our results are at the highest temperature yet reported for E0 (GaAs) in a reflectance experiment and the first observation of E0 (Ga1-xAlxAs) at elevated temperatures. From the latter, the Varshni coefficients [Physica 34, 149 (1967)] for Ga0.82Al0.18As were determined. [ABSTRACT FROM AUTHOR]

The amplitude of the photoreflectance (PR) spectra of the direct gap of semi-insulating GaAs has been studied as a function of pump chopping frequency (2–4000 Hz) and temperature (25–198 °C). We have been able to deduce a temperature-dependent trap time and hence trap activation energy of 0.70±0.05 eV. Our experiment demonstrates that PR can be used as a contactless method to study deep traps in semiconductors, analogous to deep level transient spectroscopy. [ABSTRACT FROM AUTHOR]

Examines the micro-electroreflectance (ER) and photoreflectance (PR) characterization of the bias dependence of the quantum confined Stark effect (QCSE). Use of ER and PR; Consequences of the QCSE; Relationship between the applied bias and internal field.