E. L. Piner

PHASE SEPARATION IN INGAN GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION

We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 μm were analyzed by θ–2θ x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with <28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN.

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.

PHASE SEPARATION AND ORDERING COEXISTING IN INXGA1-XN GROWN BY METAL ORGANIC CHEMICAL VAPOR DEPOSITION

We have recently reported the occurrence of phase separation in InxGa1−xN samples with x>0.25. Theoretical studies have suggested that InxGa1−xN can phase-separate asymmetrically into a low InN% phase and an ordered high InN% phase. In this letter, we report on the existence of simultaneous phase separation and ordering of InxGa1−xN samples with x>0.25. In these samples, phase separation was detected by both transmission electron microscopy selected area diffraction (TEM-SAD) and x-ray diffraction. Ordering was detected by both imaging and TEM-SAD.

Undoped and doped GaN thin films deposited on high-temperature monocrystalline AlN buffer layers on vicinal and on-axis α (6H)–SiC(0001) substrates via organometallic vapor phase epitaxy

Monocrystalline GaN(0001) thin films have been grown at 950 °C on high-temperature, ≈ 100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 °C on α (6H)−SiC(0001) Si substrates via OMVPE in a cold-wall, vertical, pancake-style reactor. These films were free of low-angle grain boundaries and the associated oriented domain microstructure. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound excitonic emission with a FWHM value of 4 meV. The near band-edge emission from films on the vicinal substrates was shifted slightly to a lower energy, indicative of films containing residual tensile stresses. A peak attributed to free excitonic emission was also clearly observed in the on-axis spectrum. Undoped films were too resistive for accurate Hall-effect measurements. Controlled n -type, Si-doping in GaN was achieved for net carrier concentrations ranging from approximately 1 × 10 17 cm −3 to 1 × 10 20 cm −3 . Mg-doped, p -type GaN was achieved with n A −n D ≈ 3 × 10 17 cm −3 , ρ ≈ 7 Ω · cm, and μ ≈ 3 cm 2 /V · s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 μ m GaN films revealed FWHM values of 58 and 151 arcsec for deposition on on-axis and off-axis 6H−SiC(0001) Si substrates, respectively. The corresponding FWHM values for the AlN buffer layers were approximately 200 and 400 arcsec, respectively.

Growth and characterization of In-based nitride compounds

Abstract Development of In-based nitride compounds is lagging behind the corresponding Al- and Ga-based compounds. Potential problems facing the growth of Inx Ga1 − x N films and their double heterostructures will be outlined. A tentative model which describes the reaction pathways taking place during the growth of these In-based nitride compounds is presented and is used to explain both our ALE and MOCVD results. In addition, growth parameters leading to the achievement of high values of x, reduction of In metal incorporation and improvement of both the structural and optical properties of InGaN, AlGaInN and InN will be discussed. Properties of AlGaN/InGaN/AlGaN and AlGaInN/InGaN/AlGaInN double heterostructures will be presented, with emission wavelengths in the 400–550 nm range.

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.

OPTICAL MEMORY EFFECT IN GAN EPITAXIAL FILMS

We report on memory effects in the optical properties of GaN and AlN epitaxial-films grown by atmospheric pressure metal organic chemical vapor deposition. After exposing selected areas of particular samples with He–Cd laser light (3.8 eV), we observed a persistent and marked decrease in the near band edge photoluminescence (PL) intensity emitted from these areas. This effect has been observed in epitaxial films that typically have a pyramidlike hillock surface. This ability to modulate PL emission intensity at individual points in these materials can be exploited as a method for optical data storage. A means of erasing information stored using this effect has also been investigated using lower energy (∼2 eV).

Impurity dependence on hydrogen and ammonia flow rates in InGaN bulk films

H, C, and O impurity concentrations in metalorganic chemical vapor deposition grown InGaN were found to be dependent on the hydrogen and NH3 flow rates. By increasing the hydrogen flow rate from 0 to 100 sccm, a decrease of greater than two orders of magnitude in the C and O impurity levels and one order of magnitude in the H impurity level was observed. Increasing the NH3 flow rate from 1 to 5 slm results in a decrease in the C concentration and an increase in the H and O concentrations indicating that high purity NH3 (99.999%) can be a significant source of O contamination. Additional studies show that when the InN percent in the InGaN films increases, the impurity concentrations increase regardless of changes in the growth conditions. The InGaN films were grown from 710 to 780 °C and the impurity concentrations were characterized by secondary ion mass spectrometry.

Epitaxial deposition of GaInN and InN using the rotating susceptor ALE system

The growth of GaInN ternary alloys has been investigated using atomic layer epitaxy. Single crystal films have been deposited at 100 Torr in the 600°C to 700°C temperature range using the rotating susceptor approach. The InN percentage in the deposited films were found to depend on more than just the gas phase In/Ga ratio. In addition to the relative indium to gallium composition of the precursor gases, the indium incorporation was also found to depend on the absolute partial pressures of the reactant gases. The indium incorporation increases with decreasing growth temperatures, and may reach a temperature dependent saturation limit for a given set of growth conditions. Optimization of the ALE growth process has resulted in single crystal films exhibiting band edge room temperature photoluminescence for InN percentages of up to 27% in the GaInN ternary films. In addition, single crystal indium nitride has been grown using the ALE technique at 480°C.