Temperature-induced switching-over of the luminescence transitions in GaInNAs/GaAs quantum wells

Photoluminescence (PL) spectra of the GaInNAs/GaAs single quantum well (SQW) with different N compositions are carefully studied in a range of temperatures and excitation power densities. The anomalous S-shape temperature dependence of the PL peak is analysed based on the competition and switching-over between the peaks related to N-induced localized states and the peak related to interband excitonic recombination. It is found that with increasing N composition, the localized energy increases and the turning point of the S-shape temperature dependence occurs at higher temperature, where the localized carriers in the bandtail states obtain enough thermal activation energy to be dissociated and delocalized. The rapid thermal annealing (RTA) effectively reduces the localized energy and causes a decrease of the switching-over temperature.

Mode characteristics of semiconductor equilateral triangle microcavities with side length of 5-20 mu m

Semiconductor equilateral triangle microresonators (ETRs) with side length of 5, 10, and 20 mum are fabricated by the two-step inductively coupled plasma (ICP) etching technique. The mode properties of fabricated InGaAsP ETRs are investigated experimentally by photoluminescence (PL) with the pumping source of a 980-nm semiconductor laser and distinct peaks are observed in the measured PL spectra. The wavelength spacings of the distinct peaks agree very well with the theoretical longitudinal mode intervals of the fundamental transverse modes in the ETRs, which verifies that the distinct peaks are corresponding to the enhancement of resonant modes. The mode quality factors are calculated from the width of the resonant peaks of the PL spectra, which are about 100 for the ETR with side length of 20 mum.

Characteristics of oxide-free InGaAlAs layers grown by narrow stripe selective MOVPE

Narrow stripe selective MOVPE has been used to grow high quality oxide-free InGaAlAs layers on an InP substrate patterned with SiO2 masks at optimized growth conditions. Mirror-like surface morphologies and abrupt cross sections are obtained in all samples without spike growth at the mask edge. For the narrow stripe selectively grown InGaAlAs layers with a mesa width of about 1.2 mu m, a bandgap wavelength shift of 70 nm, a photoluminescence (PL) intensity of more than 80% and a PL full width at half maximum (FWHM) of less than 60 meV are obtained simultaneously with a small mask width variation from 0 to 40 mu m. The characteristics of the thickness enhancement ratio and the PL spectrum dependence on the mask width are presented and explained by considering both the migration effect from a masked region and the lateral vapour diffusion effect.

1.3 mu m InAs/GaAs self-assembled quantum dots grown on In0.2Ga0.8As-GaAs combined strain-buffer layer

Optical properties and surface structures of InAs/CaAs self-assembled quantum dots (QDs) grown on 2 nm In-0.2 Ga0.8As and x ML GaAs combined strain-buffer layer were investigated systematically by photoluminescence ( PL) and atomic force microscopy (AFM). The QD density increased from similar to 1.7 x 10(9) cm(-2) to similar to 3.8 x 10(9) cm(-1) due to the decreasing of the lattice mismatch. The combined layer was of benefit to increasing In incorporated into dots and the average height-to-width ratios, which resulted in the red-shift of the emission peaks. For the sample of x = 10 ML, the ground state transition is shifted to 1350 nm at room temperature.

Thermal quenching of luminescence from buried and surface InGaAs self-assembled quantum dots with high sheet density

Variable-temperature photoluminescence (PL) spectra of Si-doped self-assembled InGaAs quantum dots (QDs) with and without GaAs cap layers were measured. Narrow and strong emission peak at 1075 nm and broad and weak peak at 1310 nm were observed for the buried and surface QDs at low temperature, respectively. As large as 210 meV redshift of the PL peak of the surface QDs with respect to that of the buried QDs is mainly due to the change of the strain around QDs before and after growth of the GaAs cap layer. Using the developed localized-state luminescence model, we quantitatively calculate the temperature dependence of PL peaks and integrated intensities of the two samples. The results reveal that there exists a large difference in microscopic mechanisms of PL thermal quenching between two samples. (c) 2005 American Institute of Physics.

The effect of In content on high-density InxGa1-xAs quantum dots

We have successfully grown self-assembled InxGa1-xAs (x = 0.44, 0.47, 0.50) quantum dots (QDs) with high density (> 10(11)/cm(2)) by MBE. The effect of In content on the high-density QD is investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectra. It is found that sample with In-mole-fraction of 0.5 shows small size fluctuation and high PL intensity. The influence of growth temperature on high-density QD is also investigated in our experiment. (c) 2005 Elsevier B.V. All rights reserved.

Optical properties of phase-separated GaN1-xPx alloys grown by light-radiation heating metal-organic chemical vapour deposition

Based on the results of the temperature-dependent photoluminescence (PL) measurements, the broad PL emission in the phase-separated GaNP alloys with P compositions of 0.03, 0.07, and 0.15 has investigated. The broad PL peaks at 2.18, 2.12 and 1.83 eV are assigned to be an emission from the optical transitions from several trap levels, possibly the iso-electronic trap levels related to nitrogen. With the increasing P composition (from 0.03 to 0.15), these iso-electronic trap levels are shown to become resonant with the conduction band of the alloy and thus optically inactive, leading to the apparent red shift (80-160meV) of the PL peak energy and the trend of the red shift is strengthened. No PL emission peak is observed from the GaN-rich GaNP region, suggesting that the photogenerated carriers in the GaN-rich GaNP region may recombine with each other via non-radiation transitions.

Optical properties of highly strained GaInAs/GaAs quantum wells grown by Sb assistance

Optical properties of highly strained GaInAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy with Sb assistance are investigated. The samples grown by Sb incorporation and Sb pre-deposition methods display high room-temperature photoluminescence (PL) intensity at extended long wavelength. This result is explained by the surfactant effects of Sb during the growth of GaInAs/GaAs QW systems. An abnormal S-shaped temperature dependence of the PL peak position is found in the In0.42Ga0.58As/GaAs triple QWs sample grown with Sb pre-deposition. By investigating the transmission electron microscope images and time-resolved PL spectra, it is found that the S-shaped temperature dependence of the PL peak position originates from the exciton localization effect brought by the Sb-rich clusters on the QW interface.

Optical properties and exciton localization in GaNas/GaAs

GaNAs/GaAs single quantum wells (SQWs) and dilute GaNAs bulk grown by molecular beam epitaxy(MBE) were studied by photoluminescence (PL), selectively-excited PL, and time-resolved PL. Exciton localization and delocalization were investigated in detail. Under short pulse laser excitation, the delocalization exciton emission was revealed in GaNAs/GaAs SQWs. It exhibits quite different optical properties from N-related localized states. In dilute GaNAs bulk, a transition of alloy band related recombination was observed by measuring the PL dependence on temperature and excitation intensity and time-resolved PL, as well. This alloy-related transition presents intrinsic optical properties. These results are very important for realizing the abnomal features of III-V-N semiconductors.

Sulfur-induced exciton localization in Te-rich ZnSTe alloy

Exciton localization in Te-rich ZnSTe epilayers has been studied by photoluminescence (PL) and time-resolved PL. The sulfur-related exciton emission is found to dominate the radiative recombination at low temperature and is shifted to the low energy with the increase of S concentration. By measuring the PL dependence on temperature and by analyzing the PL decay process, we have clarified the localization nature of the sulfur-related exciton emission. Furthermore, the difference of the localization effect in Te- and S-rich ZnSTe is also compared and discussed. © 2005 American Institute of Physics.

Optical properties of alloy states in GaNxAs1-x (x < 0.01)

A set of GaNxAs1-x samples with a small content of nitrogen (N) (< 1%) were investigated by continuous-wave photoluminescence (PL), pulse-wave excitation PL, and photo reflectance technology. Temperature-and excitation-dependence of PL disclosed the intrinsic band gap properties of alloy states in GaNxAs1-x, which was extremely different from the N-related impurity states. At the same time, PR spectra were also studied in this work.

Room temperature 1.25 mu m emission from high indium content InxGa1-xAs/GaAs quantum wells grown by molecular beam epitaxy

Long-wavelength high indium content InxGa1-xAs/GaAs single/multi quantum wells (QWs) structures have been successfully grown by molecular beam epitaxy. It is evidenced by X-ray measurements that the critical thickness of the well width of InxGa1-xAs/GaAs QWs with an indium content x of 47.5% can be raised up to 7nm without strain relation. 1.25μ m photoluminescence (PL) emission is obtained from the QWs with narrower full-width at half maximum (FWHM) less than 30meV. Our results are important basements which are useful for further fabricating GaAs-based long-wavelength devices. © 2005 Elsevier B.V. All rights reserved.

Luminescence properties of multi-layer InGaN quantum dots grown on C- and R-plane sapphire substrates

In this study, we report comparative luminescence properties of multi-layer InGaN quantum dots grown on C- and R-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). High-density InGaN quantum dots (QDs) are formed on GaN templates by decreasing the growth temperature and increasing the adatom hopping-barrier through surface passivation. Atomic force microscopy (AFM) has been employed to estimate the size and height of these dots. Photoluminescence (PL) spectra recorded from (1120) InGaN QDs/(1102) sapphire show much stronger emission intensity compared to spectra recorded from (0001) InGaN QDs/(0001) sapphire. Due to the absence of strong spontaneous polarization and piezoelectric field, such (1150) InGaN QDs in the active layers would lead to high efficiency light emitting devices. (c) 2005 Elsevier B.V. All rights reserved.

Growth and characterization of InN on sapphire substrate by RF-MBE

Indium nitride (InN) films were grown on sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). Atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL) spectroscopy were used to characterize the InN films. The results show that the InN films have good crystallinity, with full-width at half-maximum (FWHM) of InN (0 0 0 2) DCXRD peak being 14 arcmin. At room temperature, a strong PL peak at 0.79eV was observed. At 1.9eV or so, no peak was observed. In addition, it is found that the InN films grown with low-temperature (LT) InN buffer layer are of better quality than those without LT-InN buffer layer. (c) 2004 Elsevier B.V. All rights reserved.

The effect of a combined InAlAs and GaAs strained buffer layer on the structure and optical property of InAs quantum dots

The character of InAs quantum dots (QD) directly deposited on a combined InAlAs-GaAs (XML) strained buffer layer (SBL) has been investigated. This growth technique realizes high-density QD (5.88 x 10(10) cm(-2)) by changing the thickness of GaAs in InAlAs-GaAs SBL. The dependence of the density and the aspect ratio of QD on the GaAs thickness has been discussed in detail. The photoluminescence (PL) measurements demonstrate an obvious redshift with the increase of GaAs thickness. In addition, the deposition of InAs QDs grown on the combined InAlAs-GaAs SBL has an important effect of the QD properties. The ordered QD array can be observed from the sample deposited by atomic layer epitaxy, of which the PL peak shows an obvious redshift in comparison to the molecular beam epitaxy (MBE) QDs when the GaAs thicknesses are equal. (c) 2004 Elsevier B.V. All rights reserved.