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Research was conducted to examine the behavior of As precipitation in low-temperature grown III-V arsenides and to correlate it with the doping level, dislocation density and crystal bond strength. Results indicate that the doping level affects the concentration of charged defects such as vacancy and antisite point defects and leads to the selective precipitation of excess As in homojunctions. Findings suggest that column III vacancies have an important role in As precipitation of low-temperature grown III-V arsenides.

Researchers used photoreflectance and transmission electron microscopy (TEM) in their study of the Fermi level of annealed low-temperature GaAs on Si-delta-doped GaAs. TEM reveals the diffusion of As precipitates across the interface between the two forms of GaAs, and the accumulation of As precipitates near the Si-delta-doped layer. The researchers accounted for this occurrence in their calculation of the Fermi level in low-temperature GaAs. The Fermi level decreased to 0.5 eV below the conduction band after an increase in the annealing temperature to 900 degrees centigrade.

The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity. [ABSTRACT FROM AUTHOR]

Collective and individual emissions from In0.5Ga0.5As quantum dots (QDs) in single-defect photonic crystal nanocavities are investigated. When the cavity mode is collectively excited by the QD ensemble, a pair of dipolelike modes with definite linear polarizations is shown. Under low excitations, single-exciton emission lines are resolved. The power dependence of individual QD emissions reveals a nearly tenfold light enhancement for on-resonance QDs. The polarization state of each individual QD is also investigated. It is found that an individual dot could excite either a pure dipole mode or a mixture of both dipole modes. This behavior can be attributed to the random distribution of QDs in the nanocavity. [ABSTRACT FROM AUTHOR]

Capacitance-voltage and current-voltage measurements are performed on Al Schottky diodes on n-type InAlAs to determine their electrical characteristics. The InAlAs epilayers are grown by step-graded buffers, subjected to ambient growth conditions, on GaAs substrates. The Al content is directly proportional to the Schottky barrier height in the diodes.

We present the scanning electron-filling modulation reflectance (SEFR) of charged In[sub 0.5]Ga[sub 0.5]As self-assembled quantum dots. The SEFR is performed by applying a small constant modulation voltage and scanning the dc bias through the quantum dot energy levels. The spectral intensity of the SEFR can be related to the electron density confined in each quantum state, which shows a good agreement with the apparent carrier concentration deduced from the capacitance-voltage measurements. In this study, we find that the transition energy of quantum-dot excited state is about 10 meV smaller than the values obtained from the photoluminescence and electron-filling modulation reflectance. This phenomenon is explained by the Coulomb interactions between the optical excited electron-hole pair and the electrons occupied in the quantum dots. [ABSTRACT FROM AUTHOR]

Examines the current-voltage characteristics of AlGaAs/gallium arsenide (GaAs)/AlGaAs double heterojunction bipolar transistors grown by molecular beam epitaxy. Effect of junction and band-gap grading on the electrical performance of molecular beam epitaxial grown AlGaAs/GaAs/AlGaAs bipolar transistors; Reasons for the improvement in the current gain and offset voltage; Main disadvantage of double-heterojunction bipolar transistors.

Examines the microanalysis on the diffraction intensity to determine the aluminum concentration for aluminum compound multiple quantum-well structures. Development of technique for monitoring of surface conditions during the growth of aluminum compound semiconductor layers; Details on the simulation; Discussion on the results of the study.

Studies the Fermi level of annealed low-temperature GaAs on Si-...doped GaAs grown by molecular beam epitaxy. Experimental procedure used; Results and discussion of the study.

Focuses on a study that examined the optical properties of In[sub0.52](Al[subx]Ga[sub1-x])[sub0.48]As epilayers with various x values using variable angle spectroscopic ellipsometry. Function of aluminum composition; Candidate for the implementation of several electronic and optical devices; Factor beneficial for laser performance; Means of measuring the refractive index of InAlGaAs.

In this communication, we present experimental evidence of the piezoelectric-field-induced quantum-confined Stark effect on In[sub 0.23]Ga[sub 0.77]N/GaN multiple quantum wells. The optical transitions in In[sub 0.23]Ga[sub 0.77]N/GaN p-i-n multiple quantum wells were studied by using electrotransmission (ET) at room temperature. Quantum-well-related signals are well resolved in our ET spectra. Since the strong internal electric field breaks the symmetry of the quantum wells, both the allowed and the forbidden transitions are observed. Clear energy blueshifts in accordance with increasing reversed bias are observed in ET spectra. The strength of piezoelectric field is found to be 1.7–1.9 MV/cm in the In[sub 0.23]Ga[sub 0.77]N strain quantum well layer, which is comparable with the measurement reported in the literature. We have shown experimentally how the piezoelectric field affects the energy shift for the strained multiple quantum wells. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the electrical characteristics of aluminum (Al) Schottky diodes on n-type In[subx]Al[sub1-x]As. Description of InAlAs epilayers; Effect of the interfacial oxide layer on the determination of Schottky barrier height; Characteristics of the Al/In[subx]Al[sub1-x]As/step-graded In[suby]Al[sub1-y]As Schottky diodes.

Presents a study which measured by time-resolved photoluminescence (PL) the minority-carrier lifetime in Al[subx]Ga[sub1] [subx]As double heterostructures grown by molecular beam epitaxy (MBE). Factors affecting aluminum gallium arsenide minority-carrier lifetime; Information on PL decay time in MBE grown double heterostructures; Details of the recombination theory.