E. A. Armour

Investigation of V-Defects and embedded inclusions in InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition on (0001) sapphire

We have examined the nature of V-defects and inclusions embedded within these defects by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM)/cathodoluminescence (CL) in InGaN/GaN multiple quantum wells (MQWs). To date, indium distribution nonuniformity in the well or GaN barrier growth temperature have been identified as the main factors responsible for the V-defect occurrence and propagation. Further complicating the matter, inclusions embedded within V-defects originating at the first InGaN-to-GaN interface have been observed under certain growth conditions. Our AFM and high-resolution SEM/CL findings provide evidence that some V-defects occur merely as direct results of barrier temperature growth, and that there are additional V-defects associated with In-rich regions, which act as sinks for further indium segregation during the MQW growth. Both types of V-defects have a tendency of promoting inclusions at low-temperature (800 °C) GaN barrier growth in an H2-free enviro...

Zinc and tellurium doping in GaAs and AlxGa1−xAs grown by MOCVD

Abstract Diethylzinc and diethyltellurium have been used as p-type and n-type dopants, respectively, for GaAs and Al x Ga 1 - x As epilayers grown by low-pressure metalorganic chemical vapor deposition. The influence of growth temperature, growth rate, and dopant mole fraction upon carrier concentration were investigated for both dopants under similar growth conditions. The V/III ratio was 50 for all the samples. It was observed that the growth parameters do not affect the mobility of doped samples for a given carrier concentration. For both Zn and Te doped layers, the carrier concentrations increased linearly with decreasing growth temperature and increasing mole fraction. For the undoped samples, higher growth rates resulted in lower background impurity incorporation and higher Hall mobilities. The Te incorporation increased with increasing growth rate; however, the Zn incorporation was reduced under similar conditions. The morphology of heavily-doped samples was found to be dependent upon growth temperature and growth rate. By varying these two parameters, mirror-smooth surface morphology was obtained for Zn-doped GaAs epilayers of 1 × 10 20 cm -3 and Te-doped GaAs epilayers of 1 × 10 19 cm -3 .

High‐power spatially coherent operation of unstable resonator semiconductor lasers with regrown lens trains

We have obtained high‐power spatially coherent operation in wide‐stripe InGaAs/GaAs/AlGaAs semiconductor lasers using a monolithic unstable resonator [consisting of diverging lens elements incorporated above an asymmetric graded‐index separate confinement heterostructure (AGRIN‐SCH)]. The fabrication involves MOCVD regrowth after wet‐chemical etching of lens‐like patterns in a GaAs layer above the active region. Pulsed output powers of 175 and 490 mW have been obtained in 170‐ and 100‐μm‐wide lasers, respectively, with spatial coherence in the near field exceeding 60%. We observe good lateral mode discrimination up to 3.5 times threshold in the 100‐μm stripes with a round‐trip magnification of 6.4.

Observation of subsurface monolayer thickness fluctuations in InGaN∕GaN quantum wells by scanning capacitance microscopy and spectroscopy

Scanning capacitance microscopy and spectroscopy combined with numerical simulations have been used to image nanoscale electronic structures in In0.30Ga0.70N∕GaN quantum-well heterostructures grown by metalorganic chemical vapor deposition. Macroscopic capacitance–voltage spectroscopy and numerical simulations indicate that, depending on the bias voltage applied, either electron or hole accumulation in the n-type quantum-well region can occur. Scanning capacitance microscope images reveal local variations in electronic properties with structure similar to that of monoatomic steps observable in surface topography. Scanning capacitance spectroscopy combined with numerical simulations indicates that the observed features correspond to variations in carrier concentration arising from monolayer fluctuations in the thickness of the subsurface In0.30Ga0.70N quantum-well layer, with thickness variations occurring over distances of tens of nanometers to a micron or more.

InGaN∕GaN single-quantum-well light-emitting diodes optical output efficiency dependence on the properties of the barrier layer separating the active and p-layer regions

We have examined the output optical efficiency dependence of InGaN∕GaN single-quantum-well (SQW) structures on the properties of the barrier layer separating the active and p-layer regions in typical metalorganic chemical vapor deposition grown light-emitting-diode (LED) devices. Based on room-temperature electroluminescence and 10–300K photoluminescence findings, the optical output of SQW LEDs was found to be extremely sensitive to narrow range variations in thickness, growth temperature, and surface roughness of the uppermost barrier layer in such devices. Applying these principles and observations, a thermally robust 465nm SQW LED with an unpackaged chip-level output power in the 5.0–6.0mW range and forward voltage <3.2V at 20mA has been achieved.

EXPERIMENTAL AND THEORETICAL ANALYSIS OF SHADOW-MASKED GROWTH USING ORGANOMETALLIC VAPOR-PHASE EPITAXY : THE REASON FOR THE ABSENCE OF FACETTING

Shadow‐masked growth using organometallic vapor‐phase epitaxy allows the creation of nonplanar regions having smoothly varying profiles devoid of macroscopic facets. The shape of these profiles is independent of gas flow direction and stripe orientation, suggesting that they are determined by lateral gas phase gradients. It is proposed that the absence of facets is due to the unique growth regime underneath the shadow mask, where organic radicals combine with group‐III surface species, temporarily returning them to the vapor phase. This process has been simulated using a two‐dimensional finite‐element analysis that accurately describes the experimental behavior. Furthermore, this hypothesis predicts other experimentally observed phenomena.

Transverse junction vertical‐cavity surface‐emitting laser

An all‐epitaxial, transverse‐junction GaAs/AlGaAs vertical‐cavity surface‐emitting laser (TJ‐VCSEL) incorporating wavelength‐resonant periodic gain is reported. Metalorganic chemical vapor deposition is used for epitaxial growth of a structure containing five GaAs quantum wells. The simple p+‐p‐n+ transverse junction is fabricated using reactive ion etching and diffusion techniques. Contacts are situated on the wafer surface resulting in a nearly planar structure. The device exhibits a room‐temperature threshold of 48 mA (pulsed) and a resolution‐limited spectral width of 0.11 nm at a 855.8 nm lasing wavelength.

Observation of In concentration variations in InGaN/GaN quantum-well heterostructures by scanning capacitance microscopy

Scanning capacitance microscopy and spectroscopy have been used to analyze nanoscale variations in electronic properties in In0.15Ga0.85N∕GaN quantum-well structures grown by metalorganic chemical vapor deposition. Scanning capacitance imaging reveals that localized regions within the In0.15Ga0.85N quantum well, up to ∼25nm in radius and present at densities in the range of 109–1010cm−2, exhibit markedly increased electron accumulation relative to surrounding areas. Spatially resolved scanning capacitance spectroscopy combined with numerical simulations indicates that these regions of enhanced electron accumulation are characterized by locally increased In concentration in the quantum well. The presence of these localized In-rich regions is correlated with reported observations of increased luminescence efficiency, presumably due to carrier localization and consequently enhanced radiative recombination, in very similarly grown samples. In addition, these results demonstrate the ability, using a surface ch...

Reduction of deep levels in MOCVD-regrown Al x Ga 1− x As interfaces by (NH 4 ) 2 S passivation and in-situ HCl etching

The effects of surface preparation usinginsitu HCl etching and (NH4)2S passivation of AlxGa1-xAs episurfaces prior to regrowth by MOCVD are analyzed by deep level transient spectroscopy (DLTS), electrochemical profiling (C-V) and room-temperature photoluminescence (PL). Four electron traps were found from the DLTS measurements; a DX-center and three traps previously reported for oxygen-contaminated MOCVD systems. Electrical and optical measurements on quantum well lasers containing a regrown interface in the optical confinement region are also presented. It is demonstrated that both (NH4)2S passivation and HClin-situ etching improve the electrical and optical quality of the regrown AlxGa1-xAs interfaces, with the best results being obtained when the two methods are used in tandem.

Semiconductor laser with unstable resonator consisting of negative cylindrical lenses

We have obtained high power single-lateral-mode operation in wide-stripe InGaAs/GaAs/A1GaAs semiconductor lasers using a monolithic unstable resonator (consisting of diverging elements incorporated above an asymmetric GRIN-SCH). The fabrication involves MOCVD regrowth after wet-chemical etching of lens-like patterns in a GaAs layer above the active region. Pulsed output powers of 175 mW and 490 mW have been obtained in 170 p.m and 100 tm wide lasers respectively, with spatial coherence in the near-field exceeding 60%. We observe good lateral mode discrimination upto 3.5 times threshold in 100 .tm stripes with a round-trip magnification of 6.4.