摘要:

We report on nonalloyed ohmic contact ton+-GaAs(≈2×1018 cm−3)with a Ti-based metal/ultrathin GaS (≈15 nm)/GaAs quasi-metal-insulator-semiconductor (QMIS) structure. The GaS film was grown by molecular beam epitaxy employing the precursor, tertiarybutyl-galliumsulfide-cubane([(t-Bu)GaS]4).ForAu/Pt/Ti/GaS/n+-GaAsQMIS structure, the as-deposited contact resistivity of low10−2 &OHgr; cm2was improved to4.1×10−6 &OHgr; cm2by low-temperature annealing at 300 °C for 10 min. With annealing, we observed the formation of TiGaS on GaAs, but did not see any alloying reaction between GaAs and metals and sulfur diffusion into GaAs. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122004

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure ofn-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 &mgr;m. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122005

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A high detectivity multiquantum well midinfrared photodetector is reported. It is based on a strain compensated InGaAs/InGaP on InP structure, using bound-to-continuum intersubband absorption, with&lgr;P=4.9 &mgr;mand ∼0.5 &mgr;m full width at half maximum. This design is unique by enabling a large critical thickness, thus increasing the quantum efficiency. Photodetectors with background-limited performance (BLIP) with detectivity ofD&lgr;*(BLIP)=3.2×1010 cmHz/Wup to 110 K, with only ten quantum well periods were implemented. Arguments are given to predict an optimized background-limited performance for this design up to 135 K. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122006

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Interdiffusion can be either increased or decreased when annealing epitaxial layers covered by an oxide of GaAs. AlGaAs/GaAs quantum wells (QWs) of different widths were grown by organometallic vapor phase epitaxy. A top layer of GaAs was thermally oxidized at 450 °C, and rapid thermal annealing (RTA) was performed at 950 °C under Ar. Photoluminescence showed that an order of magnitude increase in interdiffusion occurred in the oxide-covered QWs compared to uncovered QWs. However, when a thin layer of Al was evaporated over the oxide layer prior to RTA, the rate of interdiffusion was reduced by more than order of magnitude compared to that of uncovered QWs. Interdiffusion slows because the oxide, composed primarily ofGa2O3,is quickly reduced by Al metal during RTA to form atomic Ga andAl2O3.TheAl2O3layer formed over the QWs traps the free Ga as interstitials in the GaAs. The excess Ga interstitial concentration reduces the group III vacancy concentration, and it is this reduction in group III vacancy concentration which slows the interdiffusion rate. The results show that metallurgical reactions may be used as a tool for engineering native defect concentrations and associated diffusivities. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122007

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The depth dependent strain relaxation in photolithographically defined and reactive ion etched Si/SiGe quantum wire and dot arrays is determined by high resolution grazing incidence x-ray diffraction. The laterally periodic structures were aligned along two orthogonal [110] and [1¯10] directions on the (001) surface. By recording reciprocal space maps around the (220) and (2¯20) reciprocal lattice points, the shape and in-plane strain could be determined independently of each other. Using triple axis diffractometry and changing the effective penetration depth of the x-ray radiation between 5 and 300 nm the strain relaxation in the wires and dots could be determined depth resolved. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122008

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The electrical properties of electron beam (EB) evaporated silicon dioxide(SiO2)/n-GaN,plasma enhanced chemical vapor deposited (PECVD)SiO2/n-GaN,and PECVD silicon nitride(Si3N4)/n-GaNinterfaces were investigated using high frequency capacitance–voltage measurements. Compositions of the deposited insulating layers(SiO2andSi3N4)were analyzed using x-ray photoelectron spectroscopy. Metal-insulator-semiconductor structures were fabricated on the metalorganic chemical vapor deposition grownn-type GaN layers using EB, PECVD grownSiO2and PECVD grownSi3N4layers. Minimum interface state density(2.5×1011 eV−1 cm−2)has been observed in the PECVD grownSiO2/n-GaNinterface when it was compared with EB evaporatedSiO2/n-GaNinterface(5.3×1011 eV−1 cm−2)and PECVDSi3N4/n-GaNinterface(6.5×1011 eV−1 cm−2).The interface state density(Nf)depends on the composition of deposited insulating layers. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122009

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We show that the electrical properties of nitrogen-doped nominally undoped polycrystalline chemical vapor deposited diamond films are modified by post-deposition heating in an oxidizing atmosphere. We found that the first heating cycle in air in the temperature range of 300–673 K decreased the graphitization content still present in the diamond surface and that after the second heating cycle the electrical resistance versus temperature curves became stabilized. Using a flow of argon with residues of oxygen over the surface of the sample during the heating cycles, the stabilization of the resistance-temperature dependence also occurred but only after the fourth heating cycle. The results suggest the existence of an oxidation mechanism of the nondiamond carbon atoms present at the diamond surface. After stabilization, the deep donor ionization energy was found to beEd=1.62±0.02 eV.All results brought together strongly suggest that this level is due to single nitrogen atoms that occupy substitutional lattice sites in diamond. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122010

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have measured the time-resolved photoluminescence (PL) from a series ofInxGa1−xN/GaN (x=0.22)multiple quantum well structures at room temperature. Lifetimes longer than 1 ns(1.87±0.02 ns)were measured at room temperature. The emission lifetime was found to lengthen with increasing excitation power, this is attributed to the saturation of recombination centers. The PL decay kinetics were found to be quite sensitive to the emission wavelength. The energy dependence of the emission lifetime is attributed to nanoscale fluctuations in the indium concentration. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122043

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present quantitative calculations of the electron drift mobility in wurtzite (WZ) and zincblende (ZB) structuren-type AlGaN/GaN modulation-doped field-effect transistors. The two-dimensional character of the quantum confined carriers as well as spontaneous and piezoelectric electric field effects are fully taken into account. For given doping concentration, we find that the internal electric fields lead to a much stronger carrier confinement and higher channel densities than in standard III–V materials. For high qualityn-type heterostructures, we predict a room temperature mobility at high densities close to2000 cm2/V s.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122011

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy dopedntype with Si to the levels of1015–1020 cm−3was investigated. The room temperature electron mobility versus carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model of scattering by charged dislocations. The mechanism of this scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. It was found that in the low carrier concentration region(<1017 cm−3),the electron mobility is thermally activated with an activation energy half of that of carrier concentration. This is in agreement with the prediction of the dislocation model. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122012

出版商:AIP    

年代:1998

数据来源: AIP