摘要:

This article reports a photoreflectance study of the process‐induced strains in both dry etched CdTe/Cd0.875Mn0.125Te and GaAs/Al0.3Ga0.7As nanostructures patterned by electron beam lithography. The results show that compressive strains can be introduced in both the dry etched nanostructures and the layers underneath the etched surfaces due to the introduction of defect complexes and/or crystographic damage inflicted in the fabrication process. The effect of post dry etch thermal annealing on the strains in the dry etched nanostructures has also been studied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359123

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Both continuous and multilayer profiles of solar selective surfaces have been analyzed and optimized. The structure having the highest photothermal efficiency has two uniform absorbing layers with two antireflection layers of different refractive index materials. Interference effects were analyzed in terms of optical path length of the sublayers and their combination. The phase cancellation positions for the optimized multilayer profiles are well distributed in the solar radiation range but do not occur at wavelengths above about 2.5 &mgr;m. A study of the electric‐field distribution in these optimized profiles has shown that the sharp transition at above about 2.5 &mgr;m from low to high reflectance is due to the absence of high filling factor sublayers which can act as an effective reflecting substrate. The selective properties of the optimized multilayer structures are not particularly sensitive to the optimized graded profile for thickness variations of ±20%. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359124

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The intersubband absorption saturation in GaAs/AlGaAs quantum wells as a function of the incident power has been measured, using picosecond micropulses with a power density up to 1 GW/cm2delivered by a free‐electron laser. The absorption in a sample with a bound‐to‐bound transition was compared to the absorption in a sample with a bound‐to‐resonant transition, and it was found that the electron relaxation time in the bound‐to‐bound transition is about four times shorter than for the bound‐to‐resonant transition. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359125

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The interference oscillations in normal‐incident Fourier‐transform infrared (FTIR) spectra of AlSb/GaSb superlattices, which disturb the observation of intersub‐band transitions, have been theoretically simulated and experimentally measured. Both theoretical and experimental results show that on GaSb substrates, interference oscillations are relatively weak when using GaSb rather than AlSb as the buffer layer; and by contrast, on GaAs substrates, they are weak when using AlSb rather than GaSb as the buffer layer. Using an AlSb buffer on semi‐insulating GaAs substrates, normal‐incident intersub‐band transitions fromL1toL2sub‐bands in AlSb/GaSb superlattices have been observed by the usual FTIR technique. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359126

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The photoreflectance (PR) spectroscopy of the single quantum well InxGa1−xAs/GaAs system has been measured at various temperatures. The selection rules for the interband transitions are &Dgr;n=0, wherenis the quantum number of thenth subband in the quantum well. The symmetry forbidden transitions (&Dgr;n≠0), such as 12H(wheremnHdenotes transition between themth conduction tonth valence subband of heavy hole), were often observed in the experiments and it was attributed to the existence of the built‐in electric field in the quantum well. In this work, we change the strength of the built‐in electric field by varying the temperatures of the samples. By varying the temperatures of the samples, the strength of the field can be changed by the effect of photo‐induced voltages. The measured ratios of the intensities of 12Hto 11Htransitions decrease as the temperatures are lowered. Therefore, the existence of the built‐in electric field may account for the observations of the symmetry forbidden transition 12Hin the experiments. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359058

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Room‐temperature electroluminescence at 1.54 &mgr;m is demonstrated in erbium‐implanted oxygen‐doped silicon (27 at. % O), due to intra‐4ftransitions of the Er3+. The luminescence is electrically stimulated by biasing metal‐(Si:O, Er)‐p+silicon diodes. The 30‐nm‐thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical‐vapor deposition of SiH4and N2O, doped by ion implantation with Er to a concentration up to ≊1.5 at. %, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400 °C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≊6×10−16cm2is obtained. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359059

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Data from measurements of optical absorption, photoconductivity, dark conductivity, thermally stimulated conductivity (TSC), and thermoluminescence (TL) on samples of undoped and Ga‐doped, Czochralski‐grown Bi12GeO20single crystals are reported. The photoconductivity isntype, and the dark conductivity isptype. Undoped BGO exhibits a broad, band‐edge absorption due to the optical excitation of electrons to the conduction band which gives the samples a yellow coloration. This absorption is reduced by the addition of Ga which acts as a compensating acceptor. When illuminated with light into this absorption band, but with photons of energy less than the band gap, photoexcitation of electrons occurs. These become trapped, inducing additional absorption and photoconductivity bands and TSC signals, but not TL. Excitation with photons of energy greater than the band gap induces both TSC and TL. Examination of the TSC and TL signals as a function of excitation wavelength allows the distinction between electron and hole trapping states for which trapping parameters have been determined. In addition, dark conductivity reveals three major hole states at energies of ∼Ev+1.41, ∼Ev+0.86, and ∼Ev+0.54 eV. These are believed to be empty donor states. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359060

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The analysis of thermally stimulated conductivity (TSC) measurements performed on ‘‘pure’’ Bi12GeO20(BGO) and BGO doped with gallium is presented. The TSC data show many overlapping TSC peaks in the temperature range of interest (80–300 K) which arise from a complex array of trapping states. The TSC signals from both pure BGO and Ga‐doped BGO are similar, consisting of a series of large peaks below 160 K and many smaller overlapping peaks between 180 and 300 K. The analysis shows that the large peaks below 160 K in undoped BGO arise from two trapping centers, each characterized by a distribution of activation energies centered at ∼0.24 and ∼0.29 eV, with distribution widths of ∼0.065 eV. In the Ga‐doped BGO sample the large peak seen below 180 K arises from a single trapping center at ∼0.29 eV with a distribution width of ∼0.085 eV. Activation energies, frequency factors, and concentrations of trapping states have been determined. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359061

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Silicon nitride films were deposited at low temperatures (245–370 °C) and high deposition rates (500–1700 A˚/min) by hot filament assisted chemical vapor deposition (HFCVD). Optical properties of these amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photoluminescence excitation, and electroluminescence measurements. The optical band gap of the films was varied between 2.43 and 4.74 eV by adjusting the flow rate of the disilane source gas. Three broad peaks at 1.8, 2.4, and 3.0 eV were observed in the PL spectra from these films. A simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features. The photoluminescence intensity observed in these films was 8–10 times stronger than films deposited by plasma enhanced chemical vapor deposition, under similar conditions. The high deposition rates obtained by HFCVD is believed to introduce a large number of these optically active defects. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359062

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The microstructures of low‐temperature polycrystalline silicon grown both on SiO2and Corning 7059 glass substrate are presented. The silicon was deposited by the hydrogen dilution method using electron‐cyclotron‐resonance chemical‐vapor deposition at 250 °C without any thermal annealing. The hydrogen dilution ratios were varied from 90% to 99%. Transmission electron microscopy images, Raman shift spectra, and x‐ray‐diffraction (XRD) patterns of the films were obtained. The maximum grain size was about 1 &mgr;m and the crystalline fraction which was characterized from Raman shift spectra was near 100%. From the XRD patterns ⟨111⟩‐ and ⟨110⟩‐oriented crystalline silicon grains were clearly present in the polycrystalline silicon films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359063

出版商:AIP    

年代:1995

数据来源: AIP