摘要:

InAs/GaSb superlattices sandwiched between conventional InAs layers were grown by low pressure metal organic chemical vapor deposition. Period and roughness of the superlattices were examined by field emission transmission electron microscopy. Room temperature infrared absorption spectra for InAs/GaSb superlattices were obtained by Fourier-transform infrared spectroscopy. The effects of varying the doping levels and thicknesses of the InAs sandwiching layers on the absorption spectra of InAs/GaSb superlattices were studied. It was found that by choice of suitable doping levels and cap/buffer thicknesses, the resulting fermi level equalization (as in normal homo or heterojunctions) thereby allowed the setting or “pinning” of the superlattice Fermi level to any desired value within the range made available by the original bulk material characteristics in conjunction with the doping conditions. When the thicknesses of the InAs sandwiching layers became less than 1 &mgr;m, the sandwiching effect and the intersubband transition decreased dramatically. The structure of the interfaces inside the superlattice was also studied. Energy dispersive spectroscopy was used to estimate interdiffusion conditions within the superlattice. The effects of different periods and purge gases on the absorption spectra were also studied. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365295

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the 77 K photoluminescence (PL) of undoped-AlxGa1−xAs(0.21⩽x⩽0.83)grown by organometallic vapor phase epitaxy. A deep broad (DB) PL band is found at 1.6–1.7 eV at a range ofxfrom 0.21 to 0.63, with a maximum intensity at aroundx=0.5.Its large full width at half-maximum(∼200 meV)suggests that this emission originates from some impurity-defect complex. The Si- and C-doping dependencies of the PL reveal that the emission disappears in Si-dopedn-type samples while it increases in intensity superlinearly with the hole concentration, thus, the emission center is C acceptor related. Furthermore, annealingAl0.52Ga0.48Assamples inH2flow eliminates the emission, while annealing inAsH3flow increases the emission. Based on these results, we have considered the doping and V/III dependencies of various major point defects present inp-type GaAs and those of the combinations of the C acceptor and these defects. It is concluded that the DB band originates from the substitutional C–As antisite complex(CAs–AsGa).Mass-action rule analysis of the complex deduces a quadratic increase in the PL intensity with hole concentration, which generally explains the experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365296

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The photoluminescence (PL) of heavily Te-doped GaSb has been investigated for different free carrier concentrations. A careful line shape analysis of the dominant free-to-bound transition has been performed using nonparabolic bands and taking into account the band tailing through the Kane model. The Fermi level and the band edge position have been determined from the fit of the PL band. Our results show that the energy gap value is significantly lower than in lightly doped and undoped material. This band-gap narrowing can be well understood taking into account both manybody interaction (exchange) and the random impurity distribution, that induces a rigid shift of the bands toward each other and tail states into the forbidden gap, respectively. Measurements have been performed at different temperatures and excitation power densities to evidence the role of the acceptor fluctuation and of the minority carrier distribution in determining the optical emission energy. Simple relations connecting the band-gap narrowing and the PL linewidth to the free carrier concentration are proposed in GaSb. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365297

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A nondestructive evaluation technique based on the detection of the real part of the excess charge carrier wave by photoluminescence in a frequency range from 5 kHz up to 12 MHz is introduced for semiconductor defect analysis. Crystalline imperfections in silicon due to wafer manufacturing and processing are investigated and the results are correlated with those obtained from conventional photothermal measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365351

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study of the photothermal signal generated by subsurface cylindrical structures is presented in two parts: theoretical modelization (Part I), and experimental measurements on calibrated samples (Part II). In this first part we develop a theoretical study of the scattering of planar and spherical thermal waves by a buried single infinite cylinder, parallel to the sample surface, as a function of its size and depth, and the thermal characteristics (thermal conductivity and diffusivity) of both the sample and cylinder. Temperature field solutions to the heat conduction equation are explored in two ways: by means of the Green’s function method and by a series expansion. We discuss the limits and accuracy provided by both types of calculations, and we compare the resulting temperature field for extended and pointlike illumination. Our study shows that photothermal methods allow one to locate and characterize the geometrical and thermal properties of the buried cylinder. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365298

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present an extensive experimental study of the photothermal signal produced by subsurface cylinders immersed in opaque solids. The results provided by three different modulated photothermal techniques (thermoreflectance, infrared radiometry, and mirage) for a variety of sample and cylinder thermal properties show very good agreement with the theoretical models presented in Part I of this work. A single subsurface cylinder can be quantitatively characterized by means of photothermal measurements (i.e., the determination of its size, depth, orientation, and thermal properties). We also present experimental data on a series of buried cylinders parallel to the surface that show multiple-scattering effects on the incident thermal wave. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365299

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon concentration controlled and not intentionally doped semi-insulating (SI) GaAs. The decrease of the PPA signal due to the photoquenching effect of EL2 is observed for a short period of illumination in the photon energy region from 1.0 to 1.3 eV. Since almost all of the carbon acceptors are compensated by deep donor EL2 in SI GaAs, electron occupancy of EL2 level can be controlled by changing the carbon acceptor concentration. It is found that the photoquenching becomes drastic with increasing the carbon concentration. After fully photoquenching, the PPA signal increases again through a local minimum by the continuous light illumination and finally exceeds the initial value before illumination until the saturation level is reached. The deep donor level EL6 and its metastable state are proposed. EL6 level donates electrons to compensate a part of carbon acceptors after EL20to EL2*transition is accomplished. The nonradiative recombination through this level generates the PPA signal. Since the PPA measurement can detect lower concentration of EL6 than that of EL2, the higher sensitivity of the PPA measurements than the optical absorption measurements is pointed out. The usefulness of the PPA technique for studying the nonradiative transition through deep levels in semiconductors is also suggested. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365300

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Refractive indices ofMgx(Zn0.48Cd0.52)1−xSecompounds grown on InP substrates were systematically investigated as a function of Mg composition(x).The refractive indices with various Mg compositions were estimated from the reflectance measurements. By approximating the refractive indices by the modified single effective oscillator method, the direct band gap energyE&Ggr;=2.03+1.45x,the dispersion energyEd=24.5−15.2x,and the oscillator energyE0=5.13−1.03xwere obtained. MgZnCdSe multilayer distributed Bragg reflectors (DBRs) designed by using the refractive indices obtained in this study were fabricated by a molecular beam epitaxy. As a result, high reflectance values over 98&percent; at 595 nm were experimentally obtained for the 30 pairsMg0.1(Zn0.48Cd0.52)0.9Se/Mg0.6(Zn0.48Cd0.52)0.4SeDBR, and the reflectance spectrum agreed with the theoretical values. Furthermore, good agreements of the experimental and the theoretical maximum reflectance of the DBRs as a function of the layer pair number are obtained. From theoretical investigations of 500–600 nm wavelength range DBRs, reflectance values of 99.9&percent; are calculated for the layer pair numbers from 30 to 40. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365301

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The temperature dependence of the energy gapEGand the binding energyRxof free excitons in single crystals ofCuInTe2have been calculated using Elliot’s model. The samples were prepared by the method of tellurization of stoichiometric Cu and In in liquid phase and the vertical Bridgman technique. The value ofRxaround 4 meV agrees quite well with that deduced from the effective mass approximation. The variation ofEGwith temperature is compared with the empirical model proposed by A. Mannogian and J. C. Woolley [Can. J. Phys.62, 285 (1984)]. The estimated value of the Debye temperature is in agreement with&THgr;D=191.4 Kreported from specific heat measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365302

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Magneto-optical measurements are strongly dependent on the polarization of the radiation as well as the interaction geometry of the light with respect to the relative orientation and direction of the magnetizationM.We performed magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements around the FeM2,3transition by measuring the difference between the reflected intensities of right and left circular polarized light (MCD) and the difference between the reflected intensities for opposite magnetization directions (MLD). From the angular variations of the MCD measurements we extracted the dielectric tensor &egr;(&ohgr;) which was then used as an input parameter to calculate the magneto-optical response of Fe in reflection MLD spectra. The experimental data around theM2,3edge show good agreement with model calculations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365303

出版商:AIP    

年代:1997

数据来源: AIP