摘要:

We discuss the procedure of calculating the density of states in the gap for amorphous silicon by integrating the excess sub‐band‐gap absorption. We show that in general the proportionality coefficient between the density of states and the integrated sub‐band‐gap absorption is not unique. The sum rule has been used improperly since integration of the excess subgap absorption is terminated either at a fixed energy or at an energy which does not include all optical transitions to the conduction band. We estimate the errors that can arise from this procedure.

ISSN:0021-8979    

DOI:10.1063/1.345198

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Effects of switched bias on the radiation response of metal‐oxide‐semiconductor (MOS) devices have been investigated. Transistors with 50‐nm gate oxides were irradiated at +10‐V bias to create a large trapped‐hole density in the oxide. Irradiation was continued under varying negative and positive biases. Very little radiation‐induced charge neutralization is observed at biases <−10 V for these devices. However, significant trapped‐hole neutralization is observed at biases from −10 to 0 V, with a broad maximum in neutralization rate from −6 to −1 V. The peak charge neutralization rate is approximately equal to the rate of trapped‐hole buildup under positive bias. This establishes an upper bound on the rate of radiation‐induced charge neutralization, and demonstrates that, under peak neutralization conditions, the effective cross section for the capture of radiation‐induced electrons by a filled hole trap is similar to the effective cross section for capture of a hole by an empty trap. Interface traps are found to build up at approximately the same rate when the oxide electric field at the Si/SiO2interface is positive, regardless of the field direction in the bulk of the oxide. This suggests that near‐interfacial hydrogen may play a key role in interface‐trap buildup in MOS devices.

ISSN:0021-8979    

DOI:10.1063/1.345199

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Large electrical polarization effects in the time photoresponse of multilayer heterostructure diodes have been observed. This phenomenon manifests itself in a displacement current spike synchronous to a dark–light transition and in an opposite spike in the light–dark one. The effect is associated with the pileup and spatial separation of photogenerated electrons and holes in the wells in the space‐charge region of the diode. At a particular forward bias voltage, the conduction photocurrent is eliminated, allowing accurate measurements of this phenomenon.

ISSN:0021-8979    

DOI:10.1063/1.345200

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe chemical modifications of GaAs surfaces which produce robust selenium layers that significantly enhance the electronic properties of the surface. The terminating layers are produced by depositing elemental selenium on GaAs surfaces under alkaline conditions followed by conversion to selenide and selenate using sodium sulfide. These selenium phases are more stable against photo‐oxidation than their sulfide counterparts. On the chemically modified surface, photoluminescence is enhanced 400× and Raman spectroscopy indicates that surface band bending has been reduced to ∼0.1 eV. X‐ray photoelectron spectroscopy reveals significant AsSe bond formation at the surface and a complicated interfacial structure with selenium present in oxidation states varying from 2−to 4+.

ISSN:0021-8979    

DOI:10.1063/1.345201

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Si‐doped GaAs layers were grown by the migration‐enhanced epitaxy (MEE) method and by the conventional molecular‐beam epitaxy (MBE) method, for the substrate temperatures between 220 and 670 °C. For the layers grown below 400 °C, the Si activation and mobility of the MEE layers are significantly higher than those of the MBE layers. For substrate temperatures above 400 °C, the MEE and MBE layers have roughly similar Si activation and mobility. The Raman and 4‐K photoluminescence spectra of the layers are consistent with the measured electron concentrations. This work suggests that for Si doping in GaAs at low substrate temperatures (below 400 °C), the MEE method is a very desirable alternative to the conventional MBE method.

ISSN:0021-8979    

DOI:10.1063/1.345202

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An improved boundary condition treatment for the time‐dependent Schro¨dinger equation applied to resonant‐tunneling diode simulation has been developed. This treatment is half‐implicit, or centered in time, and allows larger time steps than the previous explicit treatment. The method does not complicate the time‐dependent calculation since the resulting matrix is still tridiagonal.

ISSN:0021-8979    

DOI:10.1063/1.345203

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of interface roughness and island scattering on resonant tunneling time in double‐barrier structures is investigated theoretically. The scattering process degrades the resonant tunneling peak current, broadens the resonance, and hence shortens the resonant tunneling time. For thin barrier structures, the tunneling time enhancement due to the scattering is relatively small, while the resonance width is dominated by the scattering for thick barrier samples.

ISSN:0021-8979    

DOI:10.1063/1.345204

出版商:AIP    

年代:1990

数据来源: AIP