摘要:

We consider the problem of phonon instability in an electron‐phonon system of a semiconductor in a temperature field upon variation of a strong (quantizing) static magnetic field. It is found that the phonons may become unstable when certain values for the temperature gradient‐drift velocity and the magnetic field are exceeded. However, even after the thresholds are exceeded, it is predicted that there exist alternate bands of the magnetic field, in which the phonons are unstable in one band, stable in the next band, unstable again in the following band, etc. These alternate bands have their origin in the discreteness of the Landau levels of the electrons. An application is made for a GaAs sample. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363136

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Uniformly Si doped GaAs/Al0.33Ga0.67As multilayer structures have been studied by deep level transient spectroscopy (DLTS) and photocapacitance measurements. DLTS spectra showed five peaks which are related to defects in the GaAs layers. The concentration of these defects decreased with increasing layer thickness. An additional peak, which has been observed with forward bias filling pulses, is suggested to be related to defects near the surface, most probably due to defect accumulation in multilayers. Their emission and capture properties as well as photoionization cross sections have been studied. Evidence is provided that the emission and filling processes of these deep levels are modified due to the energy quantization in the conduction band and the carrier transport through the quantum structures. NoDXcenter related DLTS peaks or other features like persistent photoconductivity effects have been observed in any of our samples. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363137

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The carrier recombination rates in GaAs and strained InGaAs–GaAs single‐quantum‐well lasers of varying well width and potential depth, respectively, have been measured at 300, 195, and 77 K. For the InGaAs quantum wells (QWs), the carrier lifetime saturates at high inversion, with both the Shockley–Read (SR) lifetime and the saturation lifetime showing substantial reductions with decreasing temperature. The large reduction in the SR lifetime may be attributed to the increased effectiveness of acceptor ions as trap sites, due to the reduced carrier momentum at lower temperature. In a similar vein, the saturation lifetime is also reduced, due to the enhanced carrier confinement in the QW, brought about by the decrease in the carrier thermalization. For the GaAs QWs at 300 K, the saturation lifetime decreases as the well width is increased. The recombination rate law of bulk material is inadequate to predict the recombination rates in these QWs. Consequently, a local recombination model has been developed which accurately predicts the observed lifetime saturation behavior as a function of well width, potential depth, and temperature. Further,T0of 95 and 162 K are calculated for the shallow and deep QW lasers, respectively. This calculation suggests that it is the temperature dependence of the differential gain that is the dominant factor in setting the temperature sensitivity of the InGaAs QW lasers.

ISSN:0021-8979    

DOI:10.1063/1.363138

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Cadmium sulfide (CdS) layers were deposited from an aqueous solution of thiourea, cadmium sulfate, and ammonia on (100)n‐InP at 60–95 °C. X‐ray photoelectron spectroscopy showed that the deposition process effectively removes native oxides on InP and forms a protective layer for subsequent dielectric deposition. Surface analysis also showed that the InP surface is not P deficient following oxide deposition on CdS‐treated InP. Capacitance–voltage and conductance–voltage measurements of metal–insulator–semiconductor (MIS) capacitors were used to compare samples with and without CdS films between InP and a deposited insulator. Capacitance–voltage response of CdS‐treated MIS structures showed well‐defined regions of accumulation, depletion, and inversion. The interface‐state density at midgap was reduced from 5×1011to 6×1010eV−1 cm−2with CdS treatment. Depletion‐mode MIS field‐effect transistors made using this new passivation technique exhibited superior device performance to that of untreated samples.

ISSN:0021-8979    

DOI:10.1063/1.363139

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a systematic investigation of the effects of organic film structure on light emitting diode (LED) performance. Metal/organic film/metal LEDs were fabricated using a five ring, poly(phenylene vinylene) related oligomer as the active layer. The structure of the vacuum evaporated oligomer films was varied from amorphous to polycrystalline by changing the substrate temperature during deposition. The intrinsic properties of the oligomer films and the LED performance were measured. The measured intrinsic film properties include: optical absorption, photoluminescence (PL) spectra, PL lifetime, PL efficiency, and effective carrier mobility. The measured device characteristics include current–voltage, capacitance–voltage, electroluminescence (EL) efficiency, and the contact metal/organic film Schottky barrier heights. The optical absorption and PL properties of the films are weakly dependent on film structure but the effective carrier mobility decreases with increasing crystallinity. The EL quantum efficiency decreases by more than one order of magnitude, the drive voltage at a fixed current increases, and the electron Schottky barrier height increases as the crystallinity of the film is increased. The diode current–voltage characteristic is determined by the dominant hole current and the electroluminescence efficiency is controlled by the contact limited electron injection. These results demonstrate significant effects of organic film structure on the performance of organic LEDs. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363140

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Pd/AlxGa1−xAs Schottky contacts and their thermal reactions are studied by capacitance–voltage measurements, current–voltage measurements, and x‐ray diffraction. The thickness of AlxGa1−xAs consumed by the Pd/AlxGa1−xAs reaction during annealing was calculated. For annealing temperatures below 300 °C the Schottky characteristics of the diodes were good but the electrical junction moves into AlxGa1−xAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd in AlxGa1−xAs and the activation energy were estimated. The activation energy was found to be larger for higher Al concentration. PdAl, PdAs2, PdGa5, and Pd5Ga2were detected in the compounds formed by the Pd/AlxGa1−xAs reaction after annealing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363141

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Amorphous SiNx:H films having nitrogen contentxgreater than 1.3 were deposited at 300 °C by varying the ammonia‐to‐monosilane flow‐rate ratioRN, using plasma‐enhanced chemical‐ vapor‐deposition. The characteristics of defects in the films subjected to UV illumination and anneal treatments were investigated by electron‐spin‐resonance (ESR) measurements. The paramagnetic Si dangling bonds (DBs) with three N atom neighbors, called theK0center, were observed for an as‐deposited film withRNof 5, and the density was favorably enhanced by exposing the film to UV light or by the UV illumination subsequent to its annealing. TheK0density decreased as the film was annealed at 550 °C after the UV illumination. The mechanisms of creation and disappearance of theK0centers by the illumination and the annealing, respectively, were interpreted in terms of the potential fluctuation model. TheK0density in as‐deposited films decreased withRN, and a new three‐line spectrum was observed asRNexceeds 7. Origins of this new spectrum are discussed. The ESR spectra due to N DBs were observed for only the films subjected to the anneal/illumination sequence, and the densities of both N DBs andK0centers decreased with increasing the annealing time before the illumination. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363142

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A modified hydrodynamic model for the analysis of submicron semiconductor devices is derived from the first four moments of a Boltzmann transport equation without invoking any phenomenological relations. Instead, the balance equations are truncated using a suitable ansatz for the electron distribution function in the fourth moment equation. Both conventional and modified hydrodynamic models are applied to ann+n−n+ballistic diode, and the results are compared. The new approach successfully suppresses spurious velocity overshoot without increasing the complexity of the model. Finally, the simulation of a two‐dimensional submicron metal‐oxide‐semiconductor field‐effect transistor by the modified hydrodynamic model is presented. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363143

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A detailed investigation of excitonic states by means of one‐ and two‐photon absorption photoluminescence excitation spectroscopy in Zn1−xCdxSe/ZnSe multi‐quantum wells is reported. Ground state and excited heavy‐ and light‐hole excitons associated with then=1,2 subbands have been selectively probed exploiting the different selection rules governing one‐ and two‐photon absorption processes. Experimental exciton transition energies are found to be in good agreement with theoretical predictions when strain and confinement effects are included. The comparison between experiments and theory allowed us to single out a well defined set of band parameters and to gauge the band‐offsets in these heterostructures. Furthermore, the absorption band edge clearly evident in the two‐photon absorption photoluminescence excitation spectra allowed us to directly measure excitonic binding energies with good accuracy. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363144

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel glassy ionic conductor, lithium niobium oxynitride, was prepared in form of thin films and characterized. Thin‐film deposition was carried out by rf magnetron sputtering of LiNbO3target in nitrogen‐containing atmosphere. These films exhibit ionic conductivity of two orders higher than that of LiNbO3films, the room‐temperature conductivity being about 5×10−7S cm−1. Film structure is highly cross linked, leading to activation energy as low as 0.5 eV. Film transmittance is higher than 85% in both the visible and solar ranges, making them also suitable for use in electrochromic devices. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363145

出版商:AIP    

年代:1996

数据来源: AIP