摘要:

A new simple nondestructive method for band‐gap estimation in HgCdTe layers is presented in this work. The theoretical approach is based on a qualitative empirical model that assumes two different regions of absorption in HgCdTe. The border between the two regions, which indicates the approximate value of the band gap, is determined by differentiation of the absorption coefficient in respect to the photon energy. The approach is verified by experimental measurements on several HgCdTe layers grown by different techniques. First, the transmission is measured by Fourier transform infrared (FTIR) spectroscopy at room temperature; then, the measured data is smoothed and the absorption coefficient extracted. The absorption coefficient is then differentiated twice in respect to the photon energy which allows estimation of the average band gap and band‐gap variations within the HgCdTe layer. It appears that this simple procedure can assist in monitoring the quality of HgCdTe layers and help predicting the cutoff wavelength of HgCdTe photodiodes. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113916

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoinduced changes in the ultraviolet absorption bands of GeO2–SiO2glasses have a clear significance in photosensitive processes. In this letter, the dynamics of bleaching and growth of absorption bands in highly photosensitive germanosilicate thin films following exposure to 248 nm excimer laser radiation are discussed. Strong evidence is found in support of a single‐photon process for the bleaching of a band at 238 nm and growth of a band at 202.5 nm as a source of photosensitivity. Calculated changes in refractive index are eight times greater than those found in two‐photon‐induced grating experiments. This suggests avenues for enhancement of photosensitive effects through proper materials conditioning. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113917

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A postannealing technique was developed in order to improve the quality of SiO2films formed by a parallel‐plate remote plasma chemical vapor deposition. The wave number of the antisymmetric stretching mode of Si–O–Si bonding in the SiO2film increased from 1058 to 1069 cm−1by an annealing in H2O vapor at 270 °C. It was estimated that averaged bonding angle of Si–O–Si was widened from 137.8° to 141.0°. The annealing in the H2O vapor ambient at 270 °C for 30 min efficiently reduced the interface trap density to 2.0×1010cm−2 eV−1and the effective oxide charges density from 7×1011to 5×109cm−2for a metal‐oxide‐semiconductor (MOS) diode using the SiO2film. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113918

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Insituscanning electron microscopy reveals delayed and continuous nucleation of two‐dimensional islands in the molecular beam epitaxy of GaAs. It is found that the islands do not appear until about 1/3 of a monolayer is deposited. The mechanism is discussed in terms of site dependent successive atomic layer growth processes. Nucleation continues till the islands start to coalesce. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113919

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The spatial arrangement of electric‐field domains in heavily doped GaAs‐AlAs superlattices was investigated by depth‐resolved cathodoluminescence (CL). By measuring the CL spectra for different excitation energies of the electrons, it is shown that the high‐field domain is located near the anode. A quantitative analysis of the CL intensities suggests that there is only one domain boundary in the sample. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113920

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the electrical properties of heavily arsenic implanted GaAs, which has structural properties similar to low temperature GaAs. The electrical conduction in the lateral direction is dominated by hopping in a defect band and the resistivity after a 600 °C anneal is on the order of 103&OHgr; cm. However, the resistivity measured on ann‐i‐nstructure in the direction perpendicular to the surface is on the order of 109&OHgr; cm. This huge difference in resistivity can be explained by the lack of an electrical contact to the defect band in then‐i‐nstructure. The activation energy of the resistivity in then‐i‐nstructure is 0.74 eV. This value is close to that for bulk undoped semi‐insulating wafers, in which the Fermi level is pinned at the midgap donor, EL2. A current transient spectroscopy study of this material reveals an electron trap with an activation energy of 0.82 eV, identical to the EL2. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113921

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

High crystalline quality epitaxial CdTe(112)B/ZnTe films were deposited by molecular‐beam epitaxy directly onto vicinal Si(112) substrates, without use of GaAs interfacial layers. The films were characterized with x‐ray diffraction, optical microscopy, and wet chemical defect etching. Single crystal, twin‐free CdTe(112)B films exhibit structural quality exceeding that previously reported for CdTe(112)B heteroepitaxy on GaAs/Si(112) or GaAs(112)B substrates. X‐ray rocking curve full width at half‐maximum of 72 arcsec for CdTe(224) reflection and near‐surface etch pit densities (EPD) of 2×106cm−2have been observed for 8‐&mgr;m‐thick CdTe films. EPD depth profiles indicate that the threading dislocation density decreases with increasing II–VI epilayer thickness up to approximately 5 &mgr;m thickness and saturates at 2×106cm−2for thickness exceeding 5 &mgr;m. The CdTe epilayer orientation was observed to tilt 2° away from the Si(112) substrate orientation toward the [001] direction. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113922

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The evolution of surface band bending and surface photovoltage was monitoredinsituby photoreflectance spectroscopy during activation of the surface of epitaxial GaAs to the state of negative electron affinity by successive deposition of cesium and oxygen in a standard ‘‘yo‐yo’’ technique. Considerable variations of the band bending (by approximately 0.3 eV) and surface photovoltage (by three orders of magnitude) were observed. It was found that the maximum of photoemission quantum yield corresponded to unexpectedly small value of the band bending &Jgr;s=0.3 eV, as compared to widely accepted value of approximately 0.5 eV. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113923

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A Se chemical passivation [(NH4)2S+Se] for GaAs Schottky diodes is presented. We have found that our (NH4)2S+Se passivated Schottky diodes have more than one order of magnitude higher forward current density than the (NH4)2Sxpassivated ones. In rapid thermal annealing treatment, an initial decrease and then increase of forward current density for (NH4)2Sxpassivated diodes is observed. For the (NH4)2S+Se and (NH4)OH treated diodes, a steady decrease of Schottky barrier height with increased annealing temperature is observed. With or without annealing treatment, the (NH4)2S+Se passivated diodes have the lowest barrier height. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113924

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The ac losses are investigated on the Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3Oxsuperconducting wires in the rod and tape forms through an ac transport method and an ac magnetic method at 77 K. Experimental results show that the ac losses at 50 Hz for both rod and tape samples are mainly dominated by the hysteresis loss independent of the measuring method. However, the tape sample yields ac transport losses larger than the ac magnetic losses by about one order of magnitude, while the rod sample shows no difference between them. This discrepancy is explained by the difference in the geometry between both samples, which affects only the ac magnetic losses. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113925

出版商:AIP    

年代:1995

数据来源: AIP