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4.2 K photoluminescence (PL) and 77 K standard Hall-effect measurements were performed for In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor (HEMT) structures grown on GaAs substrates with different indium contents in the InxGa1-xAs well or different Si delta-doping concentrations. It was found that electron concentrations increased with increasing PL intensity ratio of the “forbidden” transition (the second electron subband to the first heavy-hole subband) to the sum of the “allowed” transition (the first electron subband to the first heavy-hole subband) and the forbidden transition. And electron mobilities decreased with increasing product of the average full width at half maximum of allowed and forbidden transitions and the electron effective mass in the InxGa1-xAs quantum well. These results show that PL measurements are a good supplemental tool to Hall-effect measurements in optimization of the HEMT layer structure. [ABSTRACT FROM AUTHOR]

A step-graded InAlAs buffer layer and an In[sub 0.52]Al[sub 0.48]As/In[sub 0.53]Ga[sub 0.47]As metamorphic high electron mobility transistor (MM-HEMT) structures were grown by molecular beam epitaxy on GaAs (001) substrates, and rapid thermal annealing was performed on them in the temperature range 500–800 °C for 30 s. The as-grown and annealed samples were investigated with Hall measurements, and 77 K photoluminescence. After rapid thermal annealing, the resistivities of step-graded InAlAs buffer layer structures became high. This can avoid leaky characteristics and parasitic capacitance for MM-HEMT devices. The highest sheet carrier density n[sub s] and mobility μ for MM-HEMT structures were achieved by annealing at 600 and 650°C, respectively. The relative intensities of the transitions between the second electron subband to the first heavy-hole subband and the first electron subband to the first heavy-hole subband in the MM-HEMT InGaAs well layer were compared under different annealing temperatures. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Boron carbon nitride (BCN) films were synthesized on Si (100) and fused silica substrates by radio-frequency magnetron sputtering from a B4C target in an Ar/N2 gas mixture. The BCN films were amorphous, and they exhibited an optical band gap of ~1.0 eV and p-type conductivity. The BCN films were over-coated with ZnO nanorod arrays using hydrothermal synthesis to form BCN/ ZnO-nanorods p-n heterojunctions, exhibiting a rectification ratio of 1500 at bias voltages of ±5 V. [ABSTRACT FROM AUTHOR]

After applying an electrical current pulse (ECP) to samples of Cu–Zn alloy, {111} oriented nanotwins parallel to the ECP direction in α phase grains have been observed at ambient temperature. It seems that (a) these samples have heated up to a temperature much higher than the α to β phase transformation temperature and (b) new β nuclei on the {110} planes have formed in the original α phase. As a result, with the samples being rapidly cooled, these oriented nanotwins will be formed with the β to α martensitic transformation. [ABSTRACT FROM AUTHOR]

In this letter, it is found that when the critical electric current pulse (ECP) passes through a Cu–Zn alloy with lead inclusions, those inclusions will disappear and transfer into grain boundaries or defects, forming many dispersed small particles of lead. Such kind of lead transfer can be produced by no other heat treatments than ECP. The theoretical analysis points out that this phenomenon is attributed to its specific effect on reducing considerably the diffusion activation energy of lead in the alloy. Therefore, the ECP treatment would provide a promising method to refine materials and to improve their physical properties. [ABSTRACT FROM AUTHOR]

Shubnikov–de Haas measurements were carried out for In[sub 0.52]Al[sub 0.48]As/In[sub x]Ga[sub 1-x]As metamorphic high-electron-mobility-transistor structures grown on GaAs substrates with different indium contents and/or different Si δ-doping concentrations. Zero-field (B→0) spin splitting was found in samples with stronger conduction band bending in the InGaAs well. It was shown that the dominant spin splitting mechanism is attributed to the contribution by the Rashba term. We found that zero-field spin splitting not only occurs in the ground electron subband, but also in the first excited electron subband for a sample with Si δ-doping concentration of 6×10[sup 12] cm[sup -2]. We propose that this In[sub 0.52]Al[sub 0.48]As/In[sub x]Ga[sub 1-x]As metamorphic high-electron-mobility-transistor structure grown on GaAs may be a promising candidate spin-polarized field-effect transistors. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A Shubnikov–de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i=1). Very close mobilities of 5859 and 5827 cm[sup 2]/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95×10[sup 12] cm[sup -2] due to incomplete transfer of the electrons from the Si δ-doped layer to the well. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

InAlAs/InGaAs metamorphic high-electron-mobility transistor structures with different spacer layers on GaAs substrates are characterized by Raman measurements. The influence of In[sub 0.52]Al[sub 0.48]As spacer thickness on longitudinal optic phonon–plasmon coupling is investigated. It is found that the intensity of GaAs-like longitudinal optic phonon, which couples with collective intersubband transitions of two-dimensional electron gas, is strongly affected by the different subband energy spacings, subband electron concentrations, and wave function distributions, which are determined by different spacer thicknesses. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]