C. W. Tu

Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy

The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employ ...

Direct determination of electron effective mass in GaNAs/GaAs quantum wells

Electron effective mass (m*e) in GaNxAs1-x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The m*e values of 0.12m0 and 0.19m0 are directly determi ...

Mechanism for rapid thermal annealing improvements in undoped GaNxAs1−x/GaAs structures grown by molecular beam epitaxy

A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1−x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1−x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies.

Time-resolved studies of photoluminescence in GaNxP1−x alloys: Evidence for indirect-direct band gap crossover

Time resolved photoluminescence spectroscopy is employed to monitor the effect of N incorporation on the band structure of GaNP alloys. Abrupt shortening in radiative lifetime of near-band gap emissions, arising from excitonic radiative recombination within N-related centers, is found to occur at very low N compositions of around 0.5%, i.e., within the same range as the appearance of the direct-band gap-like transitions in the photomodulated transmission spectra of GaNP reported previously. The effect has been attributed to an enhancement in oscillator strength of optical transitions due to band crossover from indirect to direct-band gap of the alloy.

Formation of nonradiative defects in molecular beam epitaxial GaNxAs1−x studied by optically detected magnetic resonance

The formation of two nonradiative defects (i.e., an AsGa-related complex and an unknown deep-level defect with g=2.03) in GaNxAs1−x epilayers and GaAs/GaNxAs1−x multiple-quantum-well structures, grown by molecular beam epitaxy, is studied by the optically detected magnetic resonance technique. It is shown that contributions by these defects in competing carrier recombination strongly vary with the nitrogen composition. An increase in the growth temperature or postgrowth rapid thermal annealing significantly reduces the influence of the nonradiative defects studied, and is accompanied by a remarkable improvement in the optical properties of the structures.

Effect of growth temperature on photoluminescence of GaNAs/GaAs quantum well structures

The effect of growth temperature on the optical properties of GaAs/GaNxAs1−x quantum wells is studied in detail using photoluminescence (PL) spectroscopies. An increase in growth temperature up to 580 °C is shown to improve the optical quality of the structures, while still allowing one to achieve high (>3%) N incorporation. This conclusion is based on: (i) an observed increase in intensity of the GaNAs-related near-band-edge emission; (ii) a reduction in band-edge potential fluctuations, deduced from the analysis of the PL line shape; and (iii) a decrease in concentration of some extended defects detected under resonant excitation of the GaNAs. The thermal quenching of the GaNAs-related PL emission, however, is almost independent of the growth temperature and is attributed to a thermal activation of an efficient nonradiative recombination channel located in the GaNAs layers.

InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAsnanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy(EDS) indicates formation of axial In x Ga 1 − x As ( x ∼ 0.20 ) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth.Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillarheterostructures is crucial for optimized device integration.

Radiative recombination mechanism in GaNxP1-x alloys

Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.

Magneto-optical and light-emission properties of III-As-N semiconductors

A brief review on our present knowledge of optical and magneto-optical properties of III-V-N alloys, in particular, Ga(In)NAs alloys with low nitrogen compositions is given. The main attention is focused on fundamental electronic parameters of the Ga(In)NAs alloys as well as key material-related issues which are relevant to device applications, such as identification of dominant recombination processes in the alloys, compositional dependence of electron effective mass and band alignment in Ga(In)NAs-based heterostructures.

Temperature dependence of the GaNxP1−x band gap and effect of band crossover

The absorption edge of GaNxP1−x alloys (0.01⩽x⩽0.03) is shown to exhibit a direct-band gap-like behavior. Thermal variation of the band gap energy Eg, however, is found to be the same or even smaller than that for the indirect band gap of GaP and depends on the N content. The effect is tentatively attributed to the following counteracting contributions to the band edge formation. An interaction with N-related localized states, especially significant in the vicinity of band crossover (e.g., x=0.013), causes a substantial slow down of the Eg shift with temperature. On the contrary, an increasing contribution of Γc states, which becomes predominant for the higher compositions, leads to the larger thermal variation in Eg.