GaAsN/GaAs and InGaAsN/GaAs heterostructures grown by molecular beam epitaxy

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 μm radiation at room temperature was demonstrated using In_0.28Ga_0.72As_0.97N_0.03/GaAs quantum wells. Pis’ma Zh. Tekh. Fiz. 24, 81–87 (December 12, 1998)     

Photoreflectance spectroscopy of InGaAsN/GaAs quantum wells grown by MBE

Highly strained In_0.28Ga_0.72As_1−xN_x/GaAs single quantum well (SQW) structures grown by molecular beam epitaxy for different N mole fractions have been investigated by photoreflectance (PR) spectroscopy at room temperature. The influence of nitrogen on the electronic structure and on the optical properties of the quantum well has been analysed. The observation of excited state transitions allowed demonstrating a type I band line-up for both heavy and light holes, for such indium and nitrogen mole fractions. All the observed optical transitions have been identified on the base of the results of the envelope function calculation including strain effects. The dependence of the optical transitions on the nitrogen content has been derived and compared with the experiment.     

InSb/InAs quantum dots grown by liquid phase epitaxy

The first original results on the growth of quantum dots (QDs) in the InSb/InAs system by liquid phase epitaxy (LPE) are reported. The density and dimensions of QDs were studied by methods of scanning probe microscopy and atomic force microscopy. The surface density, shapes, and dimensions of LPE-grown nanoislands depend on the growth conditions (temperature, cooling rate, and solution melt-substrate contact time). In the interval of temperatures T = 420–445°C, homogeneous arrays of InSb quantum dots on InAs(100) substrates were obtained with an average height of H = 3.4 ± 1nm, a radius of R = 27.2 ± 7.5 nm, and a density of up to 1.9 × 10¹⁰ cm^?2.     

Investigation of deep level traps in dilute GaAsN layers grown by liquid phase epitaxy

Dilute GaAsN layers are grown by liquid phase epitaxy (LPE) technique, using polycrystalline GaN as the source of nitrogen. A band gap lowering of 100 meV is obtained from low temperature photoluminescence (PL) measurements which correspond to a little more than 0.5% nitrogen in the layer. Using 10 K photocapacitance measurements, a 0.7 eV electron trap is detected in the material which is assigned to an interstitial (N-N)_As defect. Annealing of the material at 750 °C for 1 h greatly reduced this trap and new electron traps with activation energies of 0.8 and 0.9 eV are detected. These new traps are suggested to be due to individual nitrogen-related defect complexes, produced by the thermal annihilation of the N-N bond. After a high temperature treatment of the GaAsN growth melt with 0.1 wt.% Er, nitrogen is found to be removed from the layer and no electron trap was detected.     

Photoconverters based on GaAs/Ge heterostructures grown by low-temperature liquid phase epitaxy

A low-temperature liquid phase epitaxy technique involving rapid cooling of a solution melt has been developed for the growth of epitaxial GaAs films on germanium substrates. Using this method, it is possible to obtain high-quality submicron GaAs epilayers on Ge substrates for photoelectric converters.     

Dislocations in GaAs p-i-n diodes grown by hydride vapour phase epitaxy

Hydride vapour phase epitaxy grown all-epitaxial p-i-n structures were studied by synchrotron X-ray topography. Three types of process induced dislocations were found: short threading dislocations, long straight interfacial dislocations and circular arc dislocations. The majority of the dislocations observed are short straight threading dislocations, the density of which is typically about 5000 cm⁻². The dislocations at the p-i interface are long straight lines parallel to [110]. They are screw dislocations having their Burgers vector parallel to [110], calculated from the contrast analysis of the well resolved dislocation images. One sample also showed a dense misfit dislocation network at the n-side. However, no misfit dislocations were seen in the back-reflection topographs of the n-side of the other samples, which shows that it is possible to grow a misfit-dislocation free n-type GaAs layer onto the substrate side of a hydride vapour phase epitaxy grown GaAs surface after proper substrate removal.     

p and n-type germanium layers grown using iso-butyl germane in a III-V metal-organic vapor phase epitaxy reactor

We report on the growth of n- and p-doped Germanium (Ge) on Ge substrates by Metal-Organic Vapor Phase Epitaxy (MOVPE). Iso-butyl germane, a liquid metal-organic source less toxic than Germane, is used as Ge precursor. We demonstrate the p-doping of Germanium by MOVPE using Trimethylgallium. The influence of the growth parameters for n and p-type doping is studied in order to optimize the morphology, the structural and the electrical properties of the Ge layers. The controlled growth of p and n doped Ge layers opens the possibility to realize totally epitaxially grown Ge diodes with improved performances, for example, for solar cell applications.     

Electro-optical properties of diluted GaAsN on GaAs grown by APMOVPE

In this paper we report on the optical and electrical studies of single GaAs_1?x N _x epitaxial layers grown on GaAs substrates by means of atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). Three kinds of samples with 1.2 %, 1.6 % and 2.7 % nitrogen content were studied. Optical properties of the layers were investigated with the use of room temperature transmittance and reflectance measurements. Subsequently Schottky Au-GaAs_1?x N _x contacts were processed and characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements within 80–480 K temperature range. From the I-V and C-V characteristics the ideality factor, series resistance and built-in potential were determined. Obtained diodes can be used for further studies on defects with the use of DLTS method.     

Effect of temperature on the growth of InAs/GaAs quantum dots grown on a strained GaAs layer

We have studied the effect of temperature on the growth of InAs quantum dots (QDs) grown on a strained GaAs layer. The 2.0 nm thick, strained GaAs was obtained by growing it on a relaxed In0.15Ga0.85As layer. We observed that the density of QDs grown in this manner strongly depends on the growth temperature. A change in the growth temperature from 510 degrees C to 460 degrees C resulted in a large increase in the QD density from 2.3 x 10(10) cm(-2) to 6.7 x 10(10) cm(-2) and a sharp reduction in their height from 8.0 nm to 3.0 nm. Photoluminescence (PL) results from these QDs are also presented.     

Ordered domain structures of nitrogen-doped GaInP layers grown by organometallic vapor phase epitaxy

Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies have been performed on organometallic vapor phase epitaxial GaInP heterostructures grown on (001) GaAs singular and vicinal substrates to investigate nitrogen doping effect on the ordering and domain structures. TEM results show that well-defined order–disorder–order heterostructures are formed when nitrogen doping level is high. This indicates that nitrogen hinders the occurrence of ordering. For the singular samples, ordered domain structures are found to be dependent on the nitrogen doping level of the underlying layer, on which they are grown. The doping dependence of ordered structures and the formation of anti-phase boundaries are described based on surface undulations (i.e., hillocks) and step configuration.     

Investigation of the fabrication mechanism of self-assembled GaAs quantum rings grown by droplet epitaxy

We have directly imaged the formation of a GaAs quantum ring (QR) using droplet epitaxy followed by annealing in arsenic ambient. Based on the atomic force micrograph measurement and the analysis of surface energy, we determine that the formation of self-assembled GaAs QRs is due to the gallium atom's diffusion and crystallization driven by the gradient of surface energy. The phenomenon that GaAs is etched by the gallium droplets is reported and analyzed. It has been demonstrated that the epitaxy layers, such as AlAs and InGaP, can be used as the etching stop layer and hence can be used to control the shape and height of the QRs.     

Simultaneous interface and interband lasing in InAs/InAsSbP heterostructures grown by metalorganic vapor phase epitaxy

Coherent radiation sources have been manufactured based on double heterostructures of the InAs/InAsSbP type grown by metalorganic vapor-phase epitaxy. The mode composition of the lasing spectrum is determined by simultaneous induced recombination at the heteroboundary and in the bulk of the active region, as well as nongenerated modes with intermediate frequencies. Additional optical losses at the intermediate modes decrease the slope of the laser intensity dependence on the current.     

Transformation of InAs islands to quantum ring structures by metalorganic vapor phase epitaxy

The transformation of InAs islands to quantum rings (QRs) by metalorganic vapor phase epitaxy is investigated. After covering the InAs islands with a thin GaAs partial capping layer and annealing under tertiarybutylarsine (TBAs) flow, ring-shaped nanostructures with a density of 10(7)-10(9)?cm(-2) are obtained at 500-600?°C. The effects of the growth temperature, annealing process and thickness of the partial capping layer are studied. Optimum values for the annealing time and the partial capping layer thickness were found to be 60-120?s and 0.5-2.0?nm, respectively. Low temperature photoluminescence (PL) emission peaks from islands and QRs grown at 500?°C are observed at 1.04?eV and 1.22?eV, respectively. The annealing temperature affected the QR evolution and the PL emission from the QRs due to the temperature dependence of the diffusion rate of indium atoms.     

Suspended aluminum nitride structures grown via metal organic vapor phase epitaxy

The development of III-Nitride suspended structures for Micro-Electro Mechanical Systems (MEMS) and Nano-Electro Mechanical Systems (NEMS) is challenging due to lack of selective etching techniques. Recent efforts have focused on the removal of sacrificial layers based on material properties, such as crystalline quality, bandgap, polarity, doping, etc. These techniques require several processing steps in addition to precise control over the sacrificial and functional layer properties. In this work, conditions have been identified for the growth of etch-resistant polycrystalline AlN films via Metal Organic Vapor Phase Epitaxy (MOVPE) on silicon oxide surfaces, thus allowing silicon oxide to be used as a sacrificial layer in a surface micro-machining process. The MOVPE growth conditions reported result in a well oriented crystal with superior mechanical strength demonstrated by the fabrication of unsupported AlN structures with widths from 5 μm to 110 μm and air gaps ranging from 200 nm to 800 nm. This technique simplifies the fabrication process of AlN suspended structures and is well suited for achieving group III-Nitride heteroepitaxial MEMS/NEMS systems.     

Abnormal optical behaviour of InAsSb quantum dots grown on GaAs substrate by molecular beam epitaxy

InAs(Sb) quantum dots (QDs) samples were grown on GaAs (001) substrate by Molecular Beam Epitaxy (MBE). The structural characterization by Atomic Force Microscopy (AFM) of samples shows that InAsSb islands size increases strongly with antimony incorporation in InAs/GaAs QDs and decreases with reducing the growth temperature from 520 °C to 490 °C. Abnormal optical behaviour was observed in room temperature (RT) photoluminescence (PL) spectra of samples grown at high temperature (520 °C). Temperature dependent PL study was investigated and reveals an anomalous evolution of emission peak energy (EPE) of InAsSb islands, well-known as “S-inverted curve” and attributed to the release of confined carriers from the InAsSb QDs ground states to the InAsSb wetting layer (WL) states. With only decreasing the growth temperature, the S-inverted shape was suppressed indicating a fulfilled 3D-confinement of carriers in the InAsSb/GaAs QD sample.     

Longitudinal photoconductivity of GaAs/AlGaAs quantum wires

The photoconductivity (PC) of undoped GaAs/AlGaAs quantum wires (QWRs) along the wire direction is studied for the first time. The PC spectrum reveals a strong substrate-related background as well as several small structures, some of which could be connected with the QWRs. This suggestion is confirmed by the observed polarization dependence of the PC and by photoluminescence (PL) and photoluminescence excitation (PLE) measurements on a similar sample. Prolonged pre-illumination of the sample with infrared light (hν=1.18 eV) considerably reduces the background in the PC spectrum, and makes the QWR structures better resolved.     

Mechanism of self-assembled growth of ordered GaAs nanowire arrays by metalorganic vapor phase epitaxy on GaAs vicinal substrates

We report the self-catalyzed growth of GaAs nanowire arrays by metalorganic vapor phase epitaxy (MOVPE) on GaAs vicinal substrates. The effect of substrate misorientation on the nanowire growth and the influence of growth parameters such as temperature and input V/III ratio have been studied in detail. Variation in the nanowire growth mechanism and consequential changes in the nanowire growth morphology were observed. A VLS growth mechanism with negligible effect of the vicinal surface gave rise to randomly distributed droplet-terminated GaAs nanowires at 400?°C and multiprong root-grown GaAs nanowire clusters at 500?°C with low V/III ratio. The substrate misorientation effect was dominant at 500?°C with higher V/III ratio, in which case the combined effect of the vicinal surface and the self-catalyzed Ga droplets assisted the realization of self-assembled and crystallographically oriented epitaxial nanowire arrays through the vapor-solid mechanism.     

Metalorganic vapour phase epitaxy of GaAs/AlGaAs nanoheterostructures for a quantum cascade laser

Short-period GaAs/AlGaAs superlattices, an active region, and a quantum cascade laser heterostructure have been grown by metalorganic vapor phase epitaxy, and their characteristics have been studied by high-resolution X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The heterostructures have been used to produce quantum cascade lasers emitting near 10 μm. Their output pulse power at 77 K is above 200 mW.