Optical characterization of lateral epitaxial overgrown GaN layers

Abstract

The optical properties of homoepitaxial GaN layers deposited by organometallic vapor phase epitaxy on stripe-patterned GaN films on 6H-SiC substrates have been investigated. Analysis of the spatiallyresolved Raman scattering spectra indicate an improvement in material quality of the overgrown region. Room-temperature color cathodoluminescence imaging and low-temperature photoluminescence measurements indicate that a donor and an acceptor, different from those detected in the underlying GaN/AlN/SiC substrate, have been incorporated in the epitaxial layer. Detailed photoluminescence studies of the near band-edge emission strongly suggest that Si is the additional donor detected in the homoepitaxial GaN layer. Its occurrence, along with that of an acceptor-related defect which is primarily found in the laterally overgrown region, is discussed.Recently it was demonstrated that the usual high threading dislocation density in heteroepitaxial layers can be significantly reduced using a patterned GaN film for selective homoepitaxial deposition 1,2 . In this work we report the optical and electronic properties of GaN layers selectively overgrown by metalorganic vapor phase epitaxy (MOVPE) on GaN/AlN/6H-SiC substrates.Each of the initial 1.5-2.0 µm thick GaN films was deposited on a 100 nm AlN buffer layer prepared by deposition on 6H-SiC(0001) substrates 3 . These films were subsequently covered with a 100 nm SiO 2 film which were patterned by standard lithography and chemical etching 2 . The stripe patterns included both 3 µm and 5 µm wide stripe openings oriented along 1100 and etched through the SiO 2 film. Different areas had different stripe separations which range from 3 µm to 40 µm. The patterned substrates were reinstalled in the MOVPE reactor. The amount of vertical and lateral epitaxial overgrowth (LEO) showed a strong dependence on stripe orientation and growth conditions 5 . Under optimized growth conditions rectangular crosssectional stripes were deposited on both 3 µm and 5 µm wide stripes 2 . Cross-sectional and plan view transmission electron microscope TEM micrographs of isolated stripes show that the threading dislocations originating at the GaN/AlN interface are confined to the vertical growth region (window regrowth: WR) 2 . Continuous films were achieved for both 3 µm and 5 µm wide stripes; however, we will present and discuss only the results related to isolated stripes where adjacent overgrowth regions had not coalesced.The samples were initially characterized by spatially-resolved room temperature Raman scattering (RS) using the 514 nm line of an Ar ion laser focused to a 1 µm spot size 4 . The 325 nm line of a HeCd laser which was incident either normal to or at 60 degrees from normal was the exciting source for the low-temperature PL experiments. An 0.85 m double-spectrometer with 1800 gr/mm gratings, a low noise photomultiplier, and a photon counting system were used to analyze the light emitted by the samples 5 . The PL experiments were conducted with comparable or higher spectral resolution t...

Growth of CuCl thin films by magnetron sputtering for ultraviolet optoelectronic applications

“…A large lattice mismatch between these films and the silicon substrate results in the formation of high dislocation densities and ultimately reduces the emission lifetime and reliability of the device. 5,6 CuCl has a cubic zinc-blende structure with a lattice constant, a CuCl = 5.41 Å, 7 which is close ͑mismatch Ͻ0.4%͒ to that of Si ͑a Si = 5.43 Å, diamond cubic͒. 8 This close match in the crystal system and lattice parameters of CuCl and Si opens up the possibility of realizing Si based UV photonic devices using CuCl as UV emitting layer with low defect density.…”

Fast Lateral Epitaxial Overgrowth of Gallium Nitride by Metalorganic Chemical Vapor Deposition Using a Two-Step Process

“…Although a detailed study of the optical properties is necessary to clarify the issue, the difference between the two sets of samples is most likely related to the residual strain in the LEO stripes, that is, samples B, C, and D are under slightly larger compressive stress than sample A. 8,9,10 The possibility that the incorporation of impurities depend on the stripe morphology cannot be excluded and could also explain some of the differences between the two sets of samples. Figure 2 illustrates the effect of varying the TMG and NH 3 flow rates over a wide range of conditions while exposing only the {11 2 0} facets, which brings additional insight into the mechanisms of lateral growth.…”

“…Recent studies have confirmed that the density of threading dislocations (TDs) is reduced by 3-4 orders of magnitude in the LEO material grown on 6H-SiC 1 , Al 2 O 3 2,3,4 , and Si(111) 5 substrates, and the mechanisms of threading dislocations evolution with respect to the facet configuration of the LEO stripes have been investigated. 1,4,6,7 Optical studies of LEO GaN 8,9,10 and InGaN quantum wells 9 have been reported. Finally, the use of LEO GaN has resulted in marked improvements in the lifetime of laser diodes, 11 while GaN p-n junctions, 12 InGaN single 13 and multiple 14 quantum well light emitting diodes, and GaN/AlGaN heterojunction field-effect transistors 15 fabricated on LEO GaN exhibit a ~3 orders of magnitude reduction of the leakage current compared to identical devices based on bulk GaN.…”

High-Efficiency Nitride-Based Solid-State Lighting

“…This CL characteristic has been observed in polar GaN LEO stripes. [16][17][18] The mottled area extends across the entire width of the [0001 ] stripe, which corresponds to the TEM observation of dislocation bending into the laterally overgrown regions for this stripe orientation. Even though the [0001 ] stripe shown in Fig.…”