摘要:

Energy band nonparabolicity is present in the majority of materials used in heterojunctions, quantum wells, and superlattices. In the present work we derive a simplified dispersion relation for electrons using thek⋅pmodel. We demonstrate that this dispersion relation can account for nonparabolicity in both narrow and wide gap isotropic semiconductors. We then calculate the carrier effective mass and densities of states for both two‐ and three‐dimensional electron systems. Finally, we derive a simple analytical relation between the carrier concentration and the Fermi energy in a nonparabolic two‐dimensional electron gas. Agreement with a numerical model is demonstrated, while the traditional, parabolic approximation results in a large error. The simplicity of the new approximation allows an intuitive understanding of the nonparabolicity effect in two‐dimensional systems. Therefore, the new approach should be useful for design, characterization, and modeling of quantum semiconductor devices with nonparabolic energy bands.

ISSN:0021-8979    

DOI:10.1063/1.350775

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Reaction of Au with GaAs in conventional NiAuGe/GaAs ohmic contacts results in rough interfaces, poor surface morphology, and deterioration at the edges of films. To improve these properties, ohmic contacts to GaAs were formed by heating initially discrete layers of volatile arsenic and nonvolatile gallium under a Ge–Au alloy thin film. The layer sequence beginning at the air interface was AuGe(1500 A˚)/As(500 A˚)/Ga(400 A˚), all evaporated onto chemically cleaned (100) GaAs surfaces, followed by annealing at 400 to 650 °C in forming gas. A regrown layer of highly doped GaAs was formed between the AuGe layer and the original GaAs substrate. This layer was characterized by scanning Auger electron spectroscopy, scanning electron microscopy, and electrical measurements. The carrier concentration of the regrown GaAs layer was estimated from four‐point probe data to be in the range of 1019to 1020cm−3. The specific contact resistivity for the AuGe/As/Ga/GaAs regrown at 550 °C for 10 min was ≊1.5×10−5&OHgr; cm2, which is similar to values measured for AuGe/GaAs annealed at 450 °C for 2 min. The mechanism of GaAs regrowth and ohmic contact formation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.350776

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Coherence effects appearing in the two‐terminal conductance of a series of quantum point contacts are theoretically studied for zero and finite temperatures and for arbitrary phase coherence lengths in the regime of quantized Hall effects. Experimental geometries to determine the phase coherence length are proposed and the conductance in the geometries is quantitatively analyzed by using the Landauer–Bu¨ttiker approach.

ISSN:0021-8979    

DOI:10.1063/1.350777

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A detailed study of hydrogenated amorphous silicon (a‐Si:H) surfaces before and after thermal and plasma oxidation treatments was carried out using x‐ray photoelectron spectroscopy. The thickness of the surface oxides is correlated with the electrical properties of corresponding Mo Schottky barrier structures. Oxide layers up to 1.5 nm in thickness cause a decrease of the reverse current of nearly two orders in magnitude, while the forward current is hardly affected. For oxide thicknesses above 2.0 nm a large reduction in the forward current is observed. Surprisingly, the associated tunneling probabilities of the oxide interface layers in thea‐Si:H Schottky diodes are the same as those previously reported forc‐Si‐based tunnel diodes. Tunneling in thea‐Si:H devices cannot be simply described by the properties of a rectangular barrier, which is adopted most frequently in these studies. A potential form where the barrier height increases quadratically with thickness fits the observed tunneling characteristics more quantitatively, both in absolute magnitude and oxide‐thickness dependence of the tunnel current.

ISSN:0021-8979    

DOI:10.1063/1.350778

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The interfacial chemical bonding has been investigated for GaF3and CaF2deposited on S passivated GaAs(111)A, 100, and (111)B surfaces. Synchrotron radiation excited photoelectron spectroscopy S 2pmeasurements indicate greater S surface segregation for the Ga terminated (111) A and (100) surfaces relative to the As terminated (111)B surface. This S surface segregation correlates well with the Ga—S bond strength as well as the S—Ga coordination number for the three different GaAs surfaces. X‐ray photoelectron spectroscopy measurements indicate S may act as a catalyst in the reduction of Ca2+to metallic Ca at the CaF2–S/GaAs(111)A interface. In contrast to island growth observed for the CaF2/S/GaAs system, more uniform growth is observed for the GaF3/S/GaAs system. In addition, in contrast to the CaF2/S/GaAs system, band bending is considerably reduced for all surfaces upon deposition and annealing for the GaF3/S/GaAs system.

ISSN:0021-8979    

DOI:10.1063/1.350779

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Schottky barriers of Au, Al, and Sb onn‐ andp‐type layers of Al0.5Ga0.5As0.05Sb0.95have been studied. The Schottky barriers are high for Au (1.3 eV) and Al (1.2 eV) deposited onn‐type material and very low for these metals onp‐type layers. The behavior of Sb is unique with the barrier heights being 0.6–0.7 eV for bothn‐ andp‐type AlGaAsSb. The reason for the surface Fermi‐level pinning for Au and Al could be related to a predominance of Ga‐antisite–type native acceptors at the surface, which is not the case for Sb. Sulfur treatment of the surface is shown to decrease the barrier height for Au and to increase greatly the photosensitivity of Au Schottky diodes. The same effect is observed after treatment in a hydrogen plasma. In the latter case, changes in the Schottky barrier height are correlated with passivation of native acceptors in the bulk of the Al0.5Ga0.5As0.05Sb0.95.

ISSN:0021-8979    

DOI:10.1063/1.350780

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The 3‐level charge‐pumping technique for characterizing electron and hole capture cross sections of fast interface traps in metal‐oxide−semiconductor devices is studied via quasistatic one‐dimensional numerical simulation. In general, these simulations confirm our understanding of the operation of the 3‐level technique for carrier capture and emission. The simulations show that the previously developed simplified analysis of 3‐level charge pumping is reasonably accurate in the emission regime. In contrast, previous simple analysis of the capture regime is found to be in error. For quantitatively accurate results, the effect of the trapped charge on band bending must be included. A revised analytical approach for the capture regime is developed which corrects this error.

ISSN:0021-8979    

DOI:10.1063/1.350781

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The experimentally observed dependence of effective surface recombination velocitySeffat the Si‐SiO2interface on light‐induced minority carrier excess concentration is compared with theoretical predictions of an ‘‘extended Shockley–Read–Hall (SRH) formalism.’’ The calculations of SRH‐recombination rates at the Si‐SiO2interface are based on the theory of a surface space charge layer under nonequilibrium conditions and take into account the impact of illumination level, gate metal work function, fixed oxide charge density, and the energy dependence of capture cross sections &sgr;n, &sgr;pand interface state densityDit. Applying this theory top‐type silicon surfaces covered by high quality thermal oxides, the experimentally observed strong increase ofSeffwith decreasing minority carrier excess concentration could quantitatively be attributed to the combined effect of the &sgr;n/&sgr;pratio of about 1000 at midgap and the presence of a positive fixed oxide charge densityQfof about 1×1011charges/cm2. Due to the favorable work function of aluminum, surface recombination velocities below 1 cm/s can be obtained at Al‐covered Si‐SiO2interfaces for minority carrier densities above 1013cm−3.  

ISSN:0021-8979    

DOI:10.1063/1.350782

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We propose and study a new GaSb/InAs/GaSb/AlSb/InAs broken‐gap interband tunneling diode by varying the thicknesses of the InAs layer. A twice‐higher peak current density and a three‐times‐higher peak‐to‐valley current ratio in the proposed structure with a 30‐A˚‐thick InAs layer were observed relative to the structure with no InAs layer. This result indicates that the characteristic of the negative differential resistance can be improved simply by placing a thin effective InAs barrier on the GaSb side of the GaSb/AlSb/InAs single‐barrier structure. The increase of the peak current is interpreted as the result of forming a quasi‐bound state in the GaSb well. This interpretation is supported by the observation that the current‐voltage characteristic of the proposed structure is similar to that of a conventional GaSb/AlSb/GaSb/AlSb/InAs double‐barrier interband tunneling structure.

ISSN:0021-8979    

DOI:10.1063/1.350783

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The damage induced by the passivation process has been evaluated and compared by admittance and deep level transient spectroscopies in GaInAs planar photodiodes passivated by a silicon nitride film. The comparison is based on three deposition techniques: the chemical vapor deposition (CVD), the plasma‐enhanced CVD (PECVD), and the ultraviolet activated CVD (UVCVD). Two deep levels, with properties and concentration which are found to be strongly dependent on the passivation techniques, are observed: The first, located atEc−0.35 eV is detected in PECVD and UVCVD passivated diodes and attributed to the GaInAs surface degradation resulting from the deposition process. The second, located atEc−0.19 eV appears only on CVD diodes and could be related to the high‐temperature treatment specific to this technique.

ISSN:0021-8979    

DOI:10.1063/1.350784

出版商:AIP    

年代:1992

数据来源: AIP