High-quality GaN grown by gas-source MBE

High-quality GaN epilayers were consistently obtained using a home-made gas-sourer MBE system on sapphire substrates. Room-temperature electron mobility of the grown GaN film is 300 cm(2)/V s with a background electron concentration as low as 2 x 10(17) cm(-3) The full-width at half-maximum of the GaN (0 0 0 2) double-crystal X-ray rocking curve is 6 arcmin. At low temperature (3.5 K), the FWHM of the: near-band-edge photoluminescence emission line is 10 meV. Furthermore, using piezoelectric effect alone with the high-quality films, two-dimensional electron gas was formed in a GaN/AlN/GaN/sapphire structure. Its room-temperature and low-temperature (77 K) electron mobility is 680 cm(2)/V s and 1700 cm(2)/V s, and the corresponding sheet electron density is 3.2 x 10(13) and 2.6 x 10(13) cm(-2), respectively. (C) 2001 Published by Elsevier Science.

High-quality GaN grown by gas-source MBE

High-quality GaN epilayers were consistently obtained using a home-made gas-sourer MBE system on sapphire substrates. Room-temperature electron mobility of the grown GaN film is 300 cm(2)/V s with a background electron concentration as low as 2 x 10(17) cm(-3) The full-width at half-maximum of the GaN (0 0 0 2) double-crystal X-ray rocking curve is 6 arcmin. At low temperature (3.5 K), the FWHM of the: near-band-edge photoluminescence emission line is 10 meV. Furthermore, using piezoelectric effect alone with the high-quality films, two-dimensional electron gas was formed in a GaN/AlN/GaN/sapphire structure. Its room-temperature and low-temperature (77 K) electron mobility is 680 cm(2)/V s and 1700 cm(2)/V s, and the corresponding sheet electron density is 3.2 x 10(13) and 2.6 x 10(13) cm(-2), respectively. (C) 2001 Published by Elsevier Science.

Solid source MBE growth of quantum cascade lasers

High material quality is the basis of quantum cascade lasers (QCLs). Here we report the solid source molecular beam epitaxy (MBE) growth details of realizing high quality of InGaAs/InAlAs QCL structures. Accurate control of material compositions, layer thickness, doping profile, and interface smoothness can be realized by optimizing the growth conditions. Double crystal x-ray diffraction discloses that our grown QCL structures possess excellent periodicity and sharp interfaces. High quality laser wafers are grown in a single epitaxial run. Room temperature continuous-wave (cw) operation of QCLs is demonstrated.

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum wells with higher indium content grown by molecular-beam expitaxy

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum well (QW) samples with higher (42.5%) indium content were successfully grown by molecular-beam epitaxy. The cross-sectional transmission electron microscopy measurements reveal that there are no structural defects in such high indium content QWs. The room-temperature photoluminescence peak intensity of the GaIn0.425NAs/GaAs (6 nm/20 nm) 3QW is higher than, and the full width at half maximum is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality caused by strain compensation effect of introducing N to the high indium content InGaAs epilayer. (C) 2005 American Institute of Physics.

Fermi-edge singularity observed in a modulation-doped AlGaN/GaN heterostructure

In this letter, we report on the observation of Fermi-edge singularity in a modulation-doped AlGaN/GaN heterostructure grown on a c-face sapphire substrate by NH3 source molecular beam epitaxy. The two-dimensional electron gas (2DEG) characteristic of the structure is manifested by variable temperature Hall effect measurements down to 7 K. Low-temperature photoluminescence (PL) spectra show a broad emission band originating from the recombination of the 2DEG and localized holes. The enhancement in PL intensity in the high-energy side approaching Fermi level was observed at temperatures below 20 K. At higher temperatures, the enhancement disappears because of the thermal broadening of the Fermi edge. (C) 1998 American Institute of Physics. [S0003-6951(98)02543-1].

Metamorphic InGaAs p-i-n Photodetectors with 1.75 mu m Cut-Off Wavelength Grown on GaAs

Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 mu m at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 x 10(-6) A/cm(2) at 0 V bias and 2.24 x 10(-4) A/cm(2) at a reverse bias of 5 V. At a wavelength of 1.55 mu m, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 mu m diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.

Photoluminescence investigation of InAs bimodal self-assembled quantum dots state filling

Self-assembled InAs quantum dots were prepared on GaAS(100)) substrate in a solid source molecular beam epitaxy system The distribution and topographic images of uncapped dots were studied by atomic force microscope. The statistical result shows that the quantum dots are bimodal distribution. The photoluminescence spectrum results shows that the intensity of small size quantum dots dominated, which may be due to: (1) the state density of large quantum dots lower than that of small quantum dots; (2) the carriers capture rate of large size quantum dots is small relative to that of small ones; (3) there is a large strain barrier between large quantum dots and capping layer, and the large strain is likely to produce the defect and dislocation, resulting in a probability carriers transferring from large quantum dots to small dots that is very small with temperature increasing.

The fabrication and properties of InAs/GaAs columnal islands

A columnal islands system, which was composed of three layers of self-assembled InAs/GaAs quantum dots (QDs), has been fabricated by solid-source molecular beam epitaxy (MBE) through S-K mode on a (100) semi-insulating GaAs substrate. The effects of the thickness of GaAs space layer, the growth interruption time and the amount of InAs deposition on the emission wavelength of columnal islands were presented. The image of atomic force microscopy (AFM) indicated the columnal islands with high uniformity in size and shape. At room temperature, the emission wavelength of columnal islands with different effective heights was achieved 1.32 and 1.4 mum; however, the emission wavelength of single-layer QDs with normal height was just 1. l mum. It provides a useful and intuitive approach to artificially control the emission wavelength of a QD material system.

High temperature operation of 5.5 mu m strain-compensated quantum cascaded lasers

We develop 5.5-mu m InxGa1-xAs/InyAl1-yAs strain-compensated quantum cascade lasers with InP and InGaAs cladding layers by using solid-source molecular-beam epitaxy. Pulse operation has been achieved up to 323 K (50 degrees C) for uncoated 20-mu m-wide and 2-mm-long devices. These devices display an output power of 36 mW with a duty cycle of 1% at room temperature. In continuous wave operation a record peak optical power of 10 mW per facet has been measured at 83 K.

Site controlling of InAs quantum wires on cleaved edges of AlGaAs/GaAs superlattices

Site-controlled InAs quantum wires were fabricated on cleaved edges of AlGaAs/GaAs superlattices (SLs) by solid source molecular beam epitaxy. The cleaved edge of AlGaAs/GaAs SLs acted as a nanopattern for selective overgrowth after selective etching. By just growing 2.0 ML InAs without high temperature degassing, site-controlled InAs quantum wires were fabricated on the cleaved edge. Furthermore, atomic force microscopy demonstrates the diffusion of In atoms is strong toward the [00 (1) over bar] direction on the (110) surface.

Effect of layer thickness of immiscible alloy In0.52Al0.48As on the morphology of InAs nanostructure grown on In0.52Al0.48As/InP(001)

Thickness effect of immiscible alloy InAlAs as matrix layer on the morphology of InAs nanostructure grown on InAlAs/InP (0 0 1) by solid-source molecular-beam epitaxy has been studied. Experiments demonstrate that InAs nanostructure grown on thin InAlAs matrix layer forms randomly distributed quantum dot, whereas, grown on thick InAlAs matrix layer forms one-dimension ordered mixture of quantum wire and quantum dot. This drastic modification in the nanostructure morphology is attributed to the generation of composition modulation in the immiscible InAlAs alloy with the increase of the layer thickness. (C) 2004 Elsevier B.V. All rights reserved.

Ordered InAs quantum dots with controllable periods grown on stripe-patterned GaAs substrates

GaAs (001) substrates are patterned by electron beam lithography and wet chemical etching to control the nucleation of InAs quantum dots (QDs). InAs dots are grown on the stripe-patterned substrates by solid source molecular beam epitaxy, A thick buffer layer is deposited on the strip pattern before the deposition of InAs. To enhance the surface diffusion length of the In atoms, InAs is deposited with low growth rate and low As pressure. The AFM images show that distinct one-dimensionally ordered InAs QDs with homogeneous size distribution are created, and the QDs preferentially nucleate along the trench. With the increasing amount of deposited InAs and the spacing of the trenches, a number of QDs are formed beside the trenches. The distribution of additional QDs is long-range ordered, always along the trenchs rather than across the spacing regions.

Room-temperature continuous-wave operation of InAs quantum-wire laser on InP(001) substrate

A self-assembled quantum-wire laser structure was grown by solid-source molecular beam epitaxy in an InAlGaAs-InAlAs matrix oil InP(001) substrate. Ridge-waveguide lasers were fabricated and demonstrated to operate at a heatsink temperature tip to 330 K in continuous-wave (CW) mode. The emission wavelength of the lasers with 5 mm-long cavity was 1.713 mu m at room temperature in CW mode. The temperature stability of the devices was analysed and the characteristic temperature was found to be 47 K in the mnge of 220-320 K.

Selective growth of InAs islands on patterned GaAs (100) substrate

By a combination of prepatterned substrate and self-organized growth, InAs islands are grown on the stripe-patterned GaAs (100) substrate by solid-source molecular beam epitaxy. It is found that the InAs quantum dots can be formed either on the ridge or on the sidewall of the stripes near the bottom, depending on the structure of the stripes on the patterned substrate or molecular beam epitaxy growth conditions. When a InxGa(1-x)As strained layer is grown first before InAs deposition, almost all the InAs quantum dots are deposited at the edges of the top ridge. And when the InAs deposition amount is larger, a quasi-quantum wire structure is found. The optical properties of the InAs dots on the patterned substrate are also investigated by photoluminescence. (c) 2005 Elsevier Ltd. All rights reserved.

Silicon doping induced increment of quantum dot density

Low-indium-content self-assembled InGaAs/GaAs quantum dots (SAQD) were grown using solid-source molecular beam epitaxy (MBE) and investigated by atomic force microscopy and photoluminescence (PL) spectroscopy. Silicon, which was doped at different quantum dot (QD) growth stages, markedly increased the density of QD. We obtained high density In0.35Ga0.65As/GaAs(001) quantum dots of 10(11)/cm(2) at a growth temperature of 520degreesC. PL spectra and distribution statistics show the high quality and uniformity of our silicon-doped samples. The density increment can be explained using the lattice-hardening mechanism due to silicon doping.