Influence of the AlN interlayer crystal quality on the strain evolution of GaN layer grown on Si (111)

The strain evolution in metal organic chemical vapor deposition growth of GaN on Si (111) substrate with an AlN interlayer is studied. During the growth of GaN film on AlN interlayer, the growth stress changes from compression to tension. The study shows that the density of V trenches in the AlN interlayer surface and the threading dislocations generated in the AlN interlayer have a significant influence on this strain evolution process. The dislocations generated in AlN interlayer may thread across the interface and play a key role in the strain evolution process of the GaN layer grown on AlN interlayer.

Polarized Raman scattering studies of nonpolar a-plane GaN films grown on r-plane sapphire substrates by MOCVD

Nonpolar (1120) a-plane GaN thin films were grown on r-plane (1102) sapphire substrates by low-pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a-plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in-plane stresses within the epitaxial a-plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a-plane GaN films are strain free is discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Deep level and photoluminescence studies of Er-implanted GaN films

Deep level transient spectroscopy measurements were performed on the metal organic chemical vapor deposition epitaxially grown GaN before and after the implantation with Er. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300, 0.188, 0.600 and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees for 30 min. The origins of the deep defect levels were discussed. The photoluminescence (PL) properties of Er-implanted GaN thin films were also studied. After annealing at 900 degrees for 30 min in a nitrogen flow, Er-related 1.54 mu m luminescence peaks could be observed for the Er-implanted GaN sample. Moreover, the energy-transfer and recombination processes of the Er-implanted GaN film were described. (c) 2006 Elsevier B.V. All rights reserved.

Influence of AlN interfacial layer on electrical properties of high-Al-content Al0.45Ga0.55N/GaN HEMT structure

Unintentionally doped high-Al-content Al0.45Ga0.55N/GaN high electron mobility transistor (HEMT) structures with and without AlN interfacial layer were grown by metal-organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. The effects of AlN interfacial layer on the electrical properties were investigated. At 300 K, high two-dimensional electron gas (2DEG) density of 1.66 x 10(11) cm(-2) and high electron mobility of 1346 cm(2) V-1 s(-1) were obtained for the high Al content HEMT structure with a 1 nm AlN interfacial layer, consistent with the low average sheet resistance of 287 Omega/sq. The comparison of HEMT wafers with and without AlN interfacial layer shows that high Al content AlGaN/AlN/GaN heterostructures are potential in improving the electrical properties of HEMT structures and the device performances. (c) 2006 Elsevier B.V. All rights reserved.

Characteristics of InGaN multiple quantum well blue-violet laser diodes

Studies on InGaN multiple quantum well blue-violet laser diodes have been reported. Laser structures with long-period multiple quantum wells were grown by metal-organic chemical vapor deposition. Triple-axis X-ray diffraction (TAXRD) measurements show that the multiple quantum wells were high quality. Ridge waveguide laser diodes were fabricated with cleaved facet mirrors. The laser diodes lase at room temperature under a pulsed current. A threshold current density of 3.3 kA/cm(2) and a characteristic temperature To of 145 K were observed for the laser diode.

Temperature-dependent bimodal size evolution of InAs quantum dots on vicinal GaAs(100) substrates

The effects of growth temperature on the bimodal size distribution of InAs quantum dots on vicinal GaAs(100) substrates grown by metal organic chemical vapor deposition are studied. An abnormal trend of the bimodal size evolution on temperature is observed. With the increase of the growth temperature, while the density of the large dots decreases continually, that of the small dots first grows larger when temperature was below 520 degrees C, and then exhibits a sudden decrease at 535 degrees C. The trend is explained by taking into account the presence of multiatomic steps on the substrates. Photoluminescence (PL) studies show that quantum dots on vicinal substrates have a narrower PL linewidth, a longer emission wavelength, and a larger PL intensity than those of the dots with exact substrates. (c) 2006 American Institute of Physics.

Structural and optical properties of violet InGaN/AlInGaN light-emitting diodes grown by MOCVD

High-performance violet light-emitting diodes (LEDs) with InGaN/AlInGaN multiple quantum well (MQW) active regions were grown by metal organic chemical vapor deposition (MOCVD). The interface flatness of the InGaN/AlInGaN MQWs and the emission efficiency of the LED are firstly improved with increasing Al content in the AlInGaN barrier layer, and then degraded as Al content increases further, being optimal when Al content is 0.12. Similarly, the result is optimized if the indium content is approximately 2.5% in the AlInGaN barrier layer. The mechanisms which have influences on the radiative efficiency when the Al content increases are discussed. A high output power of 7.3 mW for the violet LED at 20 mA current has been achieved. (c) 2006 Elsevier B.V. All rights reserved.

Strain evolution in GaN layers grown on high-temperature AlN interlayers

The strain evolution of the GaN layer grown on a high-temperature AlN interlayer with GaN template by metal organic chemical vapor deposition is investigated. It is found that the layer is initially under compressive strain and then gradually relaxes and transforms to under tensile strain with increasing film thickness. The result of the in situ stress analysis is confirmed by x-ray diffraction measurements. Transmission electron microscopy analysis shows that the inclination of edge and mixed threading dislocations rather than the reduction of dislocation density mainly accounts for such a strain evolution. (c) 2006 American Institute of Physics.

Diode-end-pumped passively CW mode-locked Nd : YLF laser by the LT-In0.25Ga0.75As absorber

We have demonstrated a self-staring passively continuous-wave mode-locked diode end-pumped Nd:YLF laser with a semiconductor saturable absorber mirror of single-quantum-well (In0.25Ga0.75As) grown by metal-organic chemical-vapor deposition technique at low temperature. The saturable absorber was used as nonlinear absorber and output coupler simultaneously. Stable pulse duration of 3 ps has been achieved at the repetition rate of 98 MHz. The average output power was 530 mW at 1053 nm under the incident pump power of 10 W, corresponding to the peak power of 1.8 kW and pulse energy of 5.4 nJ.

Effects of edge dislocations and intentional Si doping on the electron mobility of n-type GaN films

The effects of dislocations and Si doping on the electrical properties of n-type GaN grown by metal organic chemical vapor deposition (MOCVD) are investigated. It is found that both electron mobility and carrier concentration are strongly influenced by edge dislocations. A moderate Si doping during the GaN growth improves the electron mobility, but the best doping effect depends on the dislocation density of the sample. High quality about 4-mu m-thick MOCVD-grown GaN film with a room temperature electron mobility as high as 1005 cm(2)/V s is obtained by optimizing growth conditions. (c) 2006 American Institute of Physics.

Influence of GaAsP insertion layers on performance of InGaAsP/InGaP/AlGaAs quantum-well laser

We report on the use of very thin GaAsP insertion layers to improve the performance of an InGaAsP/InGaP/AlGaAs single quantum-well laser structure grown by metal organic chemical vapour deposition. Compared to the non-insertion structure, the full width at half maximum of photoluminescence spectrum of the insertion structure measured at room temperature is decreased from 47 to 38 nm indicating sharper interfaces. X-ray diffraction shows that the GaAsP insertion layers between AlGaAs and InGaP compensates for the compressive strain to improve the total interface. The laser performance of the insertion structure is significantly improved as compared with the counterpart without the insertion layers. The threshold current is decreased from 560 to 450mA while the slope efficiency is increased from 0.61 to 0.7W/A and the output power is increased from 370 to 940mW. The slope efficiency improved is very high for the devices without coated facets. The improved laser performance is attributed to the suppression of indium carry-over due to the use of the GaAsP insertion layers.

Improved surface morphology of stacked 1.3 mu m InAs/GaAs quantum dot active regions by introducing annealing processes

The authors report a simple but effective way to improve the surface morphology of stacked 1.3 mu m InAs/GaAs quantum dot (QD) active regions grown by metal-organic chemical vapor deposition (MOCVD), in which GaAs middle spacer and top separate confining heterostructure (SCH) layers are deposited at a low temperature of 560 degrees C to suppress postgrowth annealing effect that can blueshift emission wavelength of QDs. By introducing annealing processes just after depositing the GaAs spacer layers, the authors demonstrate that the surface morphology of the top GaAs SCH layer can be dramatically improved. For a model structure of five-layer QDs, the surface roughness with the introduced annealing processes (IAPs) is reduced to about 1.3 nm (5x5 mu m(2) area), much less than 4.2 nm without the IAPs. Furthermore, photoluminescence measurements show that inserting the annealing steps does not induce any changes in emission wavelength. This dramatic improvement in surface morphology results from the improved GaAs spacer surfaces due to the IAPs. The technique reported here has important implications for realizing stacked 1.3 mu m InAs/GaAs QD lasers based on MOCVD.

Defect influence on luminescence efficiency of GaN-based LEDs

Wafers with normal light-emitting diode structure were grown by metal organic chemical vapor deposition system. The pressure and temperature were varied during growth of buffer layer in order to grow different types of epilayers. The cathodoluminescence results show that the interface distortion of quantum well plays an important role in radiant efficiency. The electroluminescence detections indicate that the dislocations also influence the external quantum efficiency by lowering the electron injection efficiency. (c) 2006 Elsevier Ltd. All rights reserved.

High-quality multiple quantum wells selectively grown on taper-patterned substrates by ultra-low-pressure MOCVD

High quality InGaAsP/InGaAsP multiple quantum wells ( MQWs) have been selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition. A large bandgap energy shift of 46 nm and photoluminescence with FWHM less than 30 meV were obtained with a rather small mask width variation (15-30 mu m). In order to study the uniformity of the MQWs grown in the selective area, novel tapered masks were employed, and the transition effect W the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated at larger ratios of the mask width to the tapered region length.

High-quality multiple quantum wells selectively grown with tapered masks by ultra-low-pressure MOCVD

An InGaAsP/InGaAsP multiple quantum wells (MQWs) selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition was investigated in this article. A 46 nm photoluminescence peak wavelength shift was obtained with a small mask width variation (15-30 mu m). High-quality crystal layers with a photoluminescence (PL) ftill-width-at-half-maximum (FWHM) of less than 30 meV were achieved. Using novel tapered masks, the transition-effect of the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated with the larger ratio of the mask width divided to the tapered region length. (C) 2005 Elsevier B.V. All rights reserved.