K. S. Boutros

Effect of hydrogen on the indium incorporation in InGaN epitaxial films

The InN percent in metalorganic chemical vapor deposition (MOCVD) and atomic layer epitaxy (ALE) grown InGaN was found to be significantly influenced by the amount of hydrogen flowing into the reactor. The temperature ranges for this study are 710–780 °C for MOCVD, and 650–700 °C for ALE. For a given set of growth conditions, an increase of up to 25% InN in InGaN, as determined by x-ray diffraction, can be achieved by reducing the hydrogen flow from 100 to 0 sccm. Additionally, the hydrogen produced from the decomposition of ammonia does not seem to change the InN percent in the films, indicating that the ammonia decomposition rate is less than 0.1%. The phenomenon of having hydrogen control the indium incorporation was not reported in the growth of any other III–V compound previously studied.

GROWTH AND CHARACTERIZATION OF ALINGAN QUATERNARY ALLOYS

We report on the deposition of AlyInxGa1−x−yN in the (0<y<0.15) and (0<x<0.14) composition range by metalorganic chemical vapor deposition. AlInGaN quaternary alloys offer a lattice‐matched platform for InGaN‐based light emitting heterostructure devices. Epitaxial growth of AlInGaN on (0001) sapphire substrates has been achieved at 750 °C. Alloy composition, lattice constants, and band gaps were obtained by energy dispersive spectroscopy, x‐ray diffraction, and room temperature PL. Band edge emissions dominate the PL spectra of these quaternary films. Preliminary data suggest that the lattice constant of AlInGaN can be deduced from chemical composition using Vegard’s law, indicating solid solution in the grown quaternary films.

High quality InGaN films by atomic layer epitaxy

InxGa1−xN single‐crystal films were grown at 600–700 °C by atomic layer epitaxy (ALE). InGaN films with compositions of up to 27% indium were achieved. The full width at half‐maximum (FWHM) of the (0002) InxGa1−xN peak by double crystal x‐ray diffraction (DCXRD) was as small as 6 min, the lowest value reported for this ternary alloy. Strong photoluminescence band edge emission between 360 and 446 nm was observed at room temperature. These low temperature ALE grown films were achieved without the need to use excessive flows of the In organometallic source and thus demonstrate the potential for growth of this ternary alloy over the entire composition range.

Direct writing of GaAs optical waveguides by laser‐assisted chemical vapor deposition

We demonstrate the direct writing of GaAs waveguide structures by selective area deposition using laser‐assisted chemical vapor deposition (LCVD). The multimode waveguides have a Gaussian shape and a very smooth surface, and they exhibit losses as low as 5.4 dB/cm. The LCVD technique offers the capability of selective growth of independent device structures, and hence the capability of monolithic integration of these devices for optoelectronic applications.

New Buffer Layers for GaN on Sapphire by Atomic Layer and Molecular Stream Epitaxy

The current approach of depositing a low temperature then annealed AlN or GaN buffer for the growth of GaN on sapphire results in a high dislocation density. These dislocations thread through the GaN layer to the surface. Reducing their density either by growing thicker films or using a strained layer superlattice is ineffective. Two new approaches for AlN/GaN buffer layer growth for GaN on sapphire have been employed: Atomic Layer Epitaxy (ALE) and molecular Stream Epitaxy (MSE). ALE is distinguished by organo-metallic/ammonia separation while MSE is distinguished by cyclic annealing of the growing film. Both ALE and MSE enhance two dimensional growth of single crystal GaN on sapphire. The structural quality of epitaxial GaN grown on these buffer layers was studied by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The initial result for the ALE buffer shows an improved quality GaN film with lower defect densities. The MSE grown buffer layer closely resembles that of conventionally grown MOCVD buffer layers observed by others, with dislocations threading through the GaN epilayer. The effects of these buffer layers on the structural and optical properties of GaN grown on sapphire will be presented.

High speed metal‐semiconductor‐metal photodetector manufactured on GaAs by low‐temperature photoassisted metalorganic chemical vapor deposition

We report on the photoassisted metalorganic chemical vapor deposition (MOCVD) of high resistivity gallium‐arsenide at low‐temperature (LT‐GaAs). The as‐grown GaAs exhibits a resistivity of ∼106 Ω cm and has been used as the active layer of a metal‐semiconductor‐metal (MSM) Schottky‐barrier photodetector. The impulse response of the detector is 4 ps with a dark current of 4 nA at a bias of 2 V. These results are comparable to those obtained from LT‐GaAs grown by molecular beam epitaxy (MBE).

Growth of High Quality InGaN Films by Metalorganic Chemical Vapor Deposition

InGaN based optical devices can cover from the violet through orange regions of the visible spectrum. Difficulties in the growth of this alloy, which have impeded it applications, include problems such as the high vapor pressure of In, weak In-N bonds and lack of sufficient nitrogen during growth. The authors report on the MOCVD growth of In{sub x}Ga{sub 1{minus}x}N (0 < x , 0.4) on sapphire substrates in the 750--800 C temperature range. X-ray diffraction data show full width at half maximum line widths as narrow as 250 arcsec for low values of x, while films with higher InN% exhibit broader line widths. Room temperature photoluminescence spectra exhibit band edge emission, with emission from deep levels increasing with x. Preliminary investigations of AlGaN/InGaN/AlGaN double heterostructures have been conducted.

AlGaInN Quaternary Alloys by MOCVD

AlGaInN quaternary alloy based devices can cover the emission wavelength from deep UV to red. This Quaternary alloy also offers lattice matched heterostructures for both optical and microwave devices. We will report on the MOCVD growth of Al x Ga 1−x-y In y N (0 3 precursors. Chemical composition, lattice constants and bandgaps of the grown films were determined by EDS, X-ray diffraction and room temperature PL. Data indicates that the lattice constants can also be deduced using Vegards law, indicating a solid solution of this alloy. PL showed band edge emission, however emission from deep levels was also observed. Optimized growth conditions and heterostructures using this quaternary alloy will be presented.

Laser-assisted chemical vapor deposition of device-quality GaAs

Selective area epitaxial growth of gallium arsenide by laser assisted chemical vapor deposition (LCVD) offers a promising approach to in situ device fabrication and integration. By scanning a focussed Ar ion laser beam across a thermally biased substrate in the presence of arsine and an organometallic source, GaAs is selectively deposited only on areas of the substrate exposed to the laser beam at substrate temperatures in the range of 300 - 400 degree(s)C. Laser assisted chemical vapor deposition of undoped and n-type doped device quality GaAs has been demonstrated. The laser-grown undoped GaAs films are highly resistive and exhibit 77 degree(s)K PL spectra with FWHMs of < 10 meV. N-type GaAs, using silane as a dopant source, has been deposited having controllable carrier concentrations ranging from 1 (DOT) 1017 - 7 (DOT) 1018 cm-3 and room temperature mobilities between 600 - 5100 cm2/V(DOT)sec. GaAs MESFET structures have been selectively deposited using the LCVD growth technique. These devices have performance characteristics comparable to devices of similar dimensions grown by conventional techniques.

Photoassisted Selective Area Growth of III–V Compounds

Selective area epitaxial growth of gallium arsenide (GaAs) by laser assisted chemical vapor deposition (LCVD) offers a promising approach to in-situ device fabrication and integration. By scanning a focussed argon ion laser beam across a thermally biased substrate in the presence of arsine and an organometallic source, GaAs is selectively deposited only on areas of the substrate exposed to the laser at substrate temperatures in the range of 300–400° C. LCVD of undoped, n-type, and p-type device quality GaAs has been demonstrated. The laser-grown undoped GaAs films are highly resistive/semi-insulating (ρ=106 Ωcm) and exhibit 77K photoluminescence (PL) spectra. Selective p-type doping (Zn from dimethylzinc, p > 1020 cm-3) has been achieved at substrate bias temperatures (Tsub) of 300°C. Selective and controllable n-type doping (Si from silane, ~ 1017 ≤ n ≤ 7×1018cm-3) has been demonstrated for 300 ≤ Tsub ≤ 400°C with room temperature mobilities between 600 – 5100 cm2/V sec. Several electronic and optoelectronic devices such as GaAs metal-semiconductor field-effect transistors (MOSFET’s), p-i-n photodiodes and metal-semiconductor-metal (MSM) photodetectors have been selectively deposited by the LCVD growth technique. These devices have performance characteristics comparable to devices of similar dimensions grown by conventional techniques. Rib, strip-loaded, and channel optical waveguides have also been directly written by LCVD. The mode structure and light confining properties of these waveguides have been studied.