摘要:

We present Raman spectra obtained from very short period (a few atomic layers) GaAs/AlAs superlattices with asymmetrical unit cells containing two different GaAs wells. This allows us to analyze quantitatively for the first time the atomic‐scale component of the interface roughness. We demonstrate that it mainly originates at the GaAs on AlAs interface and strongly decreases with the growth temperature and the underlying AlAs layer thickness.

ISSN:0003-6951    

DOI:10.1063/1.103646

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Diamond thin films have been grown epitaxially on high‐pressure synthesized cubic boron nitride (c‐BN) particles by using dc plasma chemical vapor deposition. At the early growth stage of the film onc‐BN{111} surfaces, the island structure is observed and the number density of islands is about 1011cm−2. The growth and the coalescence of islands are also found by scanning electron microscopy observation. The continuous film is obtained at the thickness of about 2000 A˚ and the surface of the film is rather smooth. The Raman peak of the epitaxial diamond film shows the shift toward the lower wave number due to the tensile stress involved in the film.

ISSN:0003-6951    

DOI:10.1063/1.103647

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The factor &ggr;=1+(RS+RD)/Rdsis suggested to modify the expression of effective electron velocity in field‐effect transistors (FETs), whereRSandRDare the source and drain resistances, respectively, andRdsis the intrinsic drain‐to‐source resistance. Based on this modified expression &ngr;’eff= 2&pgr;LfT&ggr;, whereLis the gate length andfTis the cut‐off frequency, velocity overshoots were observed clearly at room temperature in AlxGa1−xAs/GaAs heterostructure insulated‐gate FETs with both undoped and doped channels.

ISSN:0003-6951    

DOI:10.1063/1.103622

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

F+co‐implantation at different doses and energies was performed into GaAs already implanted with Be+at high dose (1015cm−2) and low energy (20 keV), in order to reduce the beryllium diffusion during post‐implant annealing. The redistribution behavior of Be and associated electrical effects were studied by secondary‐ion mass spectrometry, transmission electron microscopy (TEM), Hall effect measurements, and current‐voltage profiling. Be outdiffusion was reduced by co‐implantation of F; more than 80% of the implanted Be was retained during rapid thermal annealing up to 850 °C. The dose and energy of the F implant strongly influenced Be electrical activation efficiency. High activation, up to 48.5%, was obtained when F was co‐implanted at high dose (1015cm−2) and low energy (10 keV). Hole profiles shown reduced electrical activation in the region where F and Be profiles overlapped and TEM studies indicated the formation of {111} coherent plates, possibly BeF2precipitates, in the same region. The reduction of Be outdiffusion in F co‐implanted samples led to high activation after annealing, and was believed to be due to chemical interaction between Be and F.

ISSN:0003-6951    

DOI:10.1063/1.103623

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have investigated thin GaAs layers capped with 20 A˚ Ge pertaining to the extent of the well known surface depletion layer in this semiconductor. Using the transmission line method, the effective surface potential of 0.78 V measured in the GaAs surface was reduced to 0.45 V by the epitaxially grown Ge cap layer. About 0.26 of the 0.45 V is due to the conduction‐band discontinuity at the Ge/GaAs heterointerface which leads to an actual surface potential of around 0.19 V. The same trend was also verified by photoreflectance and photoluminescence with variable excitation wavelengths. The results are encouraging for device applications despite the possibility that a considerable portion of the 20 A˚ Ge cap layer is oxidized.

ISSN:0003-6951    

DOI:10.1063/1.103624

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this letter we report the Arrhenius‐type dependence of the valley current density on inverse temperature in a triple‐well asymmetric resonant tunneling diode. The activation energy is found to be equal to the effective phonon energy representing the AlAs and GaAs‐like mode of AlAs in the AlxGa1−xAs barrier layers of a triple well asymmetric resonant tunneling (RT) diode operating at temperatures as high as 350 K. The data presented here correlate the longitudinal optical phonons to the excess valley current found in AlxGa1−xAs/GaAs RT devices between 200 and 350 K and raise the possibility of phonon spectroscopy of high quality barrier layers via resonant tunneling transport experiments.

ISSN:0003-6951    

DOI:10.1063/1.103625

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A first principles total energy self‐consistent pseudopotential calculation is used to predict the band offset in the lattice‐matched superlattice InAs/Al0.8Ga0.2As0.14Sb0.86. We find that inclusion of interface strain changes the character of the band offset from nominally type II to strongly type II. The predicted band offset at the minimum energy configuration is in excellent agreement with the value determined from infrared photoluminescence measurements.

ISSN:0003-6951    

DOI:10.1063/1.103626

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Significant improvements in gating of Ge surfaces are achieved with the use of thin, pseudomorphic Si interlayers. Metal‐insulator‐semiconductor structures with mid‐gap interface state densities of 5×1010cm−2eV−1and showing no hysteresis have been realized on bothn‐ andp‐type Ge. The key elements of this technology are: surface cleaning, deposition of a thin Si interlayer, and the deposition of the gate dielectric, SiO2, all of which are performedinsituand sequentially at 300 °C in a single chamber with the remote plasma technique. Ion scattering spectroscopy shows complete coverage of the Ge surface by the Si layer. X‐ray photoelectron spectroscopy shows the Si interlayer is about 18 A˚ thick. The Si interlayer prevents the interfacial oxidation of the underlying Ge.

ISSN:0003-6951    

DOI:10.1063/1.104247

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Stimulated emission in indirect band‐gap AlxGa1−xAs is observed at room temperature. This indirect stimulated emission is based on alloy disorder induced no‐phonon band‐to‐band transitions. Picosecond luminescence spectroscopy as a function of alloy composition reveals a quadratic dependence of the threshold pump intensity on the energy separation of the renormalized direct and indirect conduction bands. These threshold intensities increase exponentially with lattice temperature. The temperature dependence of the threshold intensity is much weaker than in direct band‐gap AlxGa1−xAs.

ISSN:0003-6951    

DOI:10.1063/1.103605

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report a new type of photoreflectance (PR) by means of sweeping the pump laser beam. The modulation is achieved by moving the position of the pump beam with respect to the probe beam. In the conventional photoreflectance (using a mechanical chopper) the problem is caused by photoluminescence (PL) produced by the pump light. This is particularly acute at low temperatures where the PL is large. In our novel sweeping photoreflectance (SPR) technique the pump intensity is constant. Hence the problem associated with the luminescence is eliminated. Therefore SPR spectra can be obtained at much lower temperatures than conventional PR. The signal to noise ratio in SPR is usually better than that in conventional PR. The sources of noise in both conventional and sweeping photoreflectance is also discussed.

ISSN:0003-6951    

DOI:10.1063/1.103606

出版商:AIP    

年代:1990

数据来源: AIP