Effect Of Substrate Misorientation Research Articles

Effect of substrate misorientation on the properties of p-HEMT GaAs-based nanoheterostructures formed during MOCVD epitaxy

As one of the approaches to improve p-HEMT, we studied the effect of misorientation of GaAs substrates on the surface morphology, structure, and electrical properties of pseudomorphic heterostructures, as well as the parameters of transistors based on them. In a single technological cycle, heterostructures were formed on vicinal substrates with (100) orientation and misoriented by 2o to (110) by the method of MOCVD (MOCVD) in a single technological cycle. It has been established that on misoriented substrates, the growth of structurally consistent and stressed epitaxial layers occurs according to a layered-step mechanism with the formation of macrosteps. On vicinal substrates, the formation of monatomic growth steps was observed. The comparative characteristics of p-HEMT obtained using two types of substrates are considered. Keywords: GaAs/InGaAs/GaAlAs heterostructures, MOCVD epitaxy, p-HEMT, substrate misorientation, comparative characteristics of structures and p-HEMT based on them.

Effect of Substrate Misorientation on the Structural and Optical Characteristics of In-Rich InGaAs/GaAsP Quantum Wells

InGaAs quantum well (QW) lasers have attracted significant attention owing to their considerable potential for applications in optical communications; however, the relationship between the misorientation of the substrates used to grow InGaAs QWs and the structural and optical properties of QWs is still ambiguous. In this study, In-rich InGaAs/GaAsP single QWs were grown in the same run via metal organic chemical vapor deposition on GaAs (001) substrates misoriented by 0°, 2°, and 15° toward (111). The effects of substrate misorientation on the crystal quality and structural properties of InGaAs/GaAsP were investigated by X-ray diffraction and Raman spectroscopy. The 0° substrate exhibited the least lattice relaxation, and with increasing misorientation, the degree of lattice relaxation increased. The optical properties of the InGaAs/GaAsP QWs were investigated using temperature-dependent photoluminescence. An abnormal S-shaped variation of the peak energy and inverse evolution of the spectral bandwidth were observed at low temperatures for the 2° substrate, caused by the localization potentials due to the In-rich clusters. Surface morphology observations revealed that the growth mode varied with different miscuts. Based on the experimental results obtained in this study, a mechanism elucidating the effect of substrate miscuts on the structural and optical properties of QWs was proposed and verified.

Effect of substrate misorientation on the concentration of impurities and surface morphology of an epitaxial GaN layer on N-polar GaN substrate by MOVPE

This study examines the effect of (0 0 0 −1) GaN substrate misorientation on the residual impurities and surface morphology of N-polar GaN grown by metalorganic vapor-phase epitaxy. Carbon, silicon, and oxygen concentrations decreased with increasing GaN substrate misorientation angle, with the lowest impurity concentration achieved for a misorientation angle of 2° toward the m-axis, with 6 × 1015 cm−3 carbon, 6 × 1015 cm−3 silicon, and 4 × 1017 cm−3 oxygen atoms. The oxygen concentration was measured at a depth of 0.5 μm below the wafer surface, and the oxygen concentration decreased with increasing thickness. The incorporation of carbon and oxygen revealed a strong dependence on the misorientation angle. The step distance height of the steps parallel to the [1 1 −2 0] direction (or perpendicular to the [1 −1 0 0] m-direction) was confirmed to be a double-height layer step. This phenomenon indicated that m-direction steps are stable for N-polar growth in GaN. In cases of large misorientation toward the m-axis in of the GaN substrate it was difficult to control the misorientation perpendicular to the nominal direction leading to a-axis direction by wafer bowing at wafer manufacturing. Therefore, step-bunching was generated for each symmetric m-axis due to an increase in the compound's off-angle, thus causing the surface roughness to become large.

Sapphire Substrate Geometrical Effects on III-N Blue LED Material Properties

Solid-state lighting modules based upon III-N light-emitting diodes (LEDs) are now progressing towards widespread adoption in residential and commercial applications. LED manufacturers are driving die performance and yield upwards while reducing cost. However, color binning due to the sensitivity of the human eye response, which can resolve differences in dominant wavelength within a 2 nm range, remains one of the primary yield and cost limiters. As we continue to improve and understand growth process-related reproducibility, we have observed that some of the within-wafer and wafer-to-wafer characteristics cannot be explained through known physical phenomena from the epitaxy, and are more likely related to substrate properties.In this presentation, we will analyze a set of experiments designed to understand the effect of (0001) sapphire c-plane substrate physical dimensions (thickness, diameter, bow/warp/TTV, edge beveling) and crystal properties (misorientation, surface roughness) on uniformity and reproducibility of constituent LED layers. Our initial studies have found that precisely controlled crystal misorientation (offcut) towards the m-plane is a significant factor influencing wafer-to-wafer peak wavelength variation, GaN surface roughness, and p-doping levels. Quantitative analysis of these results with respect to variation in typical substrate manufacturing capabilities will be presented; the trends are in agreement with the materials characteristics explored in our previous studies [1, 2]. Warp and bow are critical parameters for control over GaN material characteristics. Furthermore, tight control over the total thickness variation (TTV) is needed to obtain highly uniform, repeatable sub-micron dimensions used to create current patterned substrate (PSS) wafers. [1] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, J.C. Ramer, A. Parekh, and E.A. Armour, “Sapphire substrate misorientation effects on GaN nucleation layer properties”, J. Crystal Growth 272:353, (2004).[2] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, A. Parekh, J.C. Ramer, S.P. Guo, and E. Armour, “Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development”, Phys. Stat. Sol.(a) 200:71, (2003).

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.

Optimization of growth conditions for InGaAs/InAlAs/InP quantum cascade lasers by metalorganic chemical vapor deposition

We investigate the growth conditions for lattice-matched InGaAs/InAlAs/InP quantum cascade lasers (QCLs) by metalorganic chemical vapor deposition (MOCVD). Effect of substrate misorientation, growth temperature, and V/III ratios of InGaAs and InAlAs layers on the surface morphology, optical quality, and impurity incorporation were systematically studied. It was found that epitaxial layers and multi-quantum-well structures grown at 720 °C with V/III ratios of 116 for InGaAs and 21 for InAlAs on InP substrates with an off-cut angle of ∼0.06° exhibit a stable step-flow growth and low oxygen and carbon contamination. Using these conditions, a ∼11.3-μm-thick QCL with an emission wavelength at ∼9.2 μm was grown and fabricated, which demonstrated excellent structural quality and operated at room temperature in pulsed mode with a threshold current density of 2.0 kA/cm 2 and a slope efficiency of 550 mW/A.

Effect of substrate misorientation on the material properties of GaAs/Al0.3Ga0.7As tunnel diodes

The effect of substrate misorientation on the material quality of the N++–GaAs/P++–AlGaAs tunnel diodes (TDs) grown on these substrates is investigated. It is found that the misorientation influences both surface roughness and interface properties of the N++–GaAs/P++–AlGaAs TDs. Smooth surface (rms roughness: 1.54 Å) and sharp interface for the GaAs/Al0.3Ga0.7As TDs were obtained when the (100) tilted 10° off toward [111] GaAs substrate was used. Besides, the oxygen content in N++–GaAs and P++–AlGaAs layers grown on the 10° off GaAs substrates was reduced due to the reduction of sticking coefficient and number of anisotropic sites.

Properties of InAs grown on misoriented GaAs substrates by atmospheric pressure metal–organic vapor phase epitaxy

InAs epilayers were grown by atmospheric pressure metal–organic vapor phase epitaxy on GaAs (1 0 0) exactly oriented substrates and misoriented by 2° and 10° toward [1 1 1]A. The layers had varying thicknesses and were deposited under the same growth conditions. Atomic force microscopy analysis show that surface morphology depends on surface misorientation and presents a low root mean square. High resolution X-ray diffraction analysis and Hall effect measurements were preformed to check the substrate misorientation effect on the crystalline quality and electrical properties respectively.

Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development

Metal-organic chemical vapor deposition (MOCVD) epitaxial layers (n-GaN, InGaN/GaN multiple quantum well (MQW) and p-GaN) of GaN based green light emitting diodes (LEDs) structures have been sequentially grown on c-plane sapphire substrate with slight misorientation from the c plane. The qualities of these sequentially grown epitaxial layers show a strong dependence of the misorientation. Structural and optical characterization demonstrate the improved qualities of the epitaxial layers at 0.30 deg misorientation angle from c plane sapphire. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of substrate orientation on phase separation in epitaxial GaInAsSb

The effect of substrate misorientation on phase separation in Ga1−xInxAsySb1−y nominally lattice matched to GaSb is reported. The layers were grown at 575°C by organometallic vapor phase epitaxy on vicinal (001) GaSb substrates, miscut \(2^o \to (\bar 1\bar 11)A, (1\bar 11)B,\) or (101). Ga1−xInxAsySb1−y (x ~ 0.1, ~ 0.09) layers, which have 300-K photoluminescence (PL) peak emission at ~2.1 μm, grow stepbunched and exhibit minimal phase separation. The full width at half maximum of 4-K PL spectra is slightly smaller at 7 meV for layers grown on substrates miscut toward \((1\bar 11)B\) compared to 9 meV for layers grown on substrates miscut toward \((\bar 1\bar 11)A\) and (101). Ga1−xInxAsySb1−y layers with higher alloy composition (0.16≤x≤0.19, 0.14≤y≤0.17), which have 300-K PL peak emission at ~2.4 μm, have significant phase separation. These layers are characterized by increased lattice constant variations and epitaxial tilt, broad PL spectra with significant band tailing, and strong contrast modulation in transmission electron microscopy. The degree of decomposition depends on substrate miscut direction: Ga1−xInxAsySb1−y layers grown on (001) \(2^o \to (1\bar 11)B\) substrates are more homogeneous than those grown on (001) \(2^o \to (\bar 1\bar 11)A\) and (001)2°→(101) substrates. The results are attributed to the smaller adatom diffusion length on substrates miscut toward \((1\bar 11)B\).

Substrate misorientation effects on Zn 1− xMg xSe layers grown on GaAs(1 1 1) by molecular beam epitaxy

The microstructural and electronic characteristics of both undoped Zn 1− x Mg x Se epilayers and Schottky diodes grown by the molecular beam epitaxy method on different misoriented n +-type GaAs(1 1 1) substrates were systematically investigated via three measurements: transmission electron microscopy, current–voltage ( I– V), and deep level transient spectroscopy. The density of V-shaped stacking faults, originating at or near the ZnMgSe (epilayer)/GaAs (substrate) interface and extending into the whole ZnMgSe epilayer, were discovered to be affected by the angles of miscut of n +-type GaAs substrates. Evidence also revealed that more stacking faults existed in the samples with 3 and 15° angles of miscut of substrates. In these cases there were also more interface state densities created at the Au/ZnMgSe Schottky junction. Such results are suspected to be the main factors contributing to the undesirable I– V characteristics of Au/ZnMgSe Schottky diodes, including less forward conduction current density, bigger turn-on voltage, and larger reverse leakage current followed by a smaller reverse breakdown voltage.

MBE growth of antiphase GaAs films using GaAs/Ge/GaAs heteroepitaxy

Semiconductor films with periodic crystal orientation modulation have nonlinear properties useful for optical wave-mixing devices. We have developed an all-epitaxial technique for preparing orientation-patterned GaAs templates by GaAs/Ge/GaAs epitaxy and have used these to grow laterally orientation-patterned films. We have investigated the effects of substrate misorientation, substrate temperature, and prelayer to find conditions which will allow controlled MBE growth of antiphase GaAs using thin Ge interlayers. After fabricating templates from these films using lithography and etching techniques, we have regrown GaAs films with antiphase crystal orientation modulation in the plane of the film. The template-induced antiphase boundaries were observed to propagate vertically under all conditions examined.

Electron diffraction and Raman studies of the effect of substrate misorientation on ordering in the AlGaInP system

We report a systematic study of the effect of substrate orientation on the ordering in the AlGaInP system, including the Al0.52In0.48P lattice-matched ternary case. Four AlGaInP/GaAs/AlInP samples were grown by metalorganic vapor phase epitaxy under identical growth conditions on [100] substrates orientated 0°, 2°, 10° and 15° either towards the [110] or the [111] axis. The ordering in both the AlInP and the AlGaInP layers was studied by electron diffraction and the Raman scattering technique. The tendency for ordering decreased with increasing misorientation and is less for (AlxGa1−x)0.52In0.48P than for AlInP. The AlInP was found to spontaneously order even when grown after a completely disordered AlGaInP layer. The Raman results show features correlated to the electron diffraction results and hence we conclude that this technique constitutes a reliable nondestructive means of characterizing this system.

Effect of substrate misorientation on quantum-dot size distribution in the InAs/GaAs system

A study is reported of the effect of (001)GaAs substrate misorientation in the [010] direction on the distribution of MBE-grown self-assembled InAs/GaAs quantum dots in size and position in the GaAs matrix. Temperature-induced narrowing of the exciton photoluminescence line of a quantum-dot ensemble caused by redistribution of photoexcited carriers among dots of different size has been observed.

The morphology of CdTe deposited by organometallic vapor phase epitaxy: The effect of substrate misorientation

Substrate misorientation and growth temperature influence the morphology of CdTe epilayers grown by organometallic vapor phase homoepitaxy. These effects were investigated by using CdTe{100} and CdTe{100} misoriented by 2, 4, 6, and 8° toward 〈111〉Te as substrates for growth in the temperature range from 337 to 425°C. Low angle pyramidal facets appeared on films grown on the CdTe(100) surface. The number density of these pyramidal facets decreased to zero as the substrate misorientation angle increased to 4°. At higher misorientation angles, low angle protrusions, resembling fish scales, appeared on the surface. When the temperature was increased, facet size decreased but facet density increased. The film morphology at the high misorientations, however, improved remarkably with increasing temperature. Cross-sectional transmission electron microscopy provided evidence that both the faceted CdTe films and films with a mirror-like finish were epitaxial single crystals with no planar defects. Schwoebel barriers are suggested as the reason for the faceting of the surface grown on CdTe{100}.

The effect of substrate misorientation on the optical, structural, and electrical properties of GaN grown on sapphire by MOCVD

We report the growth and characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on c-plane A12O3 substrates either on-axis or intentionally misoriented 2° toward the a-plane (1120) or 5 or 9° toward the m-plane (10 10). The samples are characterized by 300K photoluminescence, cathodoluminescence, and Hall-effect measurements as well as by triple-axis x-ray diffractometry to determine the effect of the misorientation on the optical, electrical, and structural properties of heteroepitaxial undoped GaN. Ten different sample sets are studied. The data reveal enhanced photo-luminescence properties, increased electron mobility, a reduced n-type background carrier concentration, and a somewhat degraded surface morphology and crystalline quality for the misoriented samples compared to the on-axis samples.

Substrate Misorientation Effects on Epitaxial GaInAsSb

AbstractThe effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6° toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6° toward (111)B misorientation, while a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6° toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 60 toward (111)B misorientation compared to 2° toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation.

The effect of substrate misorientation on the photoluminescence properties of GaN grown on sapphire by metalorganic chemical vapor deposition

We report the growth and photoluminescence (300 and 4.2 K) characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on sapphire substrates using various growth conditions. The (0001) Al2O3 c-plane substrates are oriented exactly (0001) or misoriented either 2° towards the a plane (112̄0), 5° towards the m plane (101̄0), or 9° toward the m plane. A comparison of the 300 and 4.2 K optical characteristics of the samples grown on the different substrates indicates that a higher photoluminescence intensity is measured for the films on misoriented substrates.

Surface photoabsorption study of the effect of substrate misorientation on ordering in GaInP

Substrate orientation strongly affects Cu–Pt ordering in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. In situ surface photoabsorption (SPA) measurements were used to measure the concentration of [1̄10]-oriented P dimers, characteristic of the (2×4) reconstructed surface, as a function of substrate misorientation from (001). For substrates misoriented toward either [110] [or (111)A] or [1̄10] [or (111)B], the P-dimer concentration is found to decrease systematically as the misorientation angle increases from 0° to 15.8° at 620 °C with tertiarybutylphosphine (TBP) partial pressures of 10, 50, and 200 Pa. The P-dimer concentrations on substrates misoriented toward [110] are higher than for those misoriented toward [1̄10]. The Ga0.5In0.5P layers were found to form the Cu–Pt structure during growth. The degree of order, determined from 20 K photoluminescence measurements, shows a strong correlation with the concentration of [1̄10]-oriented P dimers. The data also clearly show the effect of step structure on Cu–Pt ordering. They indicate that [110] steps formed by misorientation toward [1̄10] enhance ordering while [1̄10] steps formed by misorientation toward [110] retard ordering.

Interface structures of InGaAs/InGaAsP/InGaP quantum well laser diodes grown by metalorganic chemical vapor deposition on GaAs substrates

We have studied the effects of substrate misorientation on the growth of strained-layer In0.18Ga0.82As quantum well laser structures with InGaAsP confinement layers and In0.5Ga0.5P cladding layers lattice matched to a GaAs substrate. Low-temperature photoluminescence (PL) and atomic force microscopy (AFM) provide evidence of a strong substrate-orientation dependence of the interface structure. The surface morphology of the InGaAs quantum well is found to be determined primarily by the underlying InGaAsP confinement layer. Structures grown on exact-(100) oriented substrates exhibit three-dimensional island surface morphology, whereas growths on (100) substrates oriented 2° towards [110] exhibit high surface roughness, possibly due to step bunching. These observations correlate well with previously reported device performance from strained quantum well laser diodes in the InGaAs/InGaAsP/InGaP material system, and can serve as a tool to optimize device performance.