S. J. Rosner

Correlation of cathodoluminescence inhomogeneity with microstructural defects in epitaxial GaN grown by metalorganic chemical-vapor deposition

We discuss the relationship between microstructure and luminescence efficiency for heteroepitaxial films of GaN grown on c-axis sapphire substrates by metalorganic chemical-vapor deposition. We directly characterize the correlation between threading dislocations as observed by transmission electron microscopy, surface morphology as observed by atomic force microscopy, and wavelength-resolved cathodoluminescence imaging. We show that the inhomogeneity in the luminescence intensity of these films near band edge can be accounted for by a simple model where nonradiative recombination at threading dislocations causes a deficiency of minority carriers and results in dark regions of the epilayer. An upper bound for average diffusion length is estimated to be 250 nm.

Structural origin of V-defects and correlation with localized excitonic centers in InGaN/GaN multiple quantum wells

In the growth of InGaN/GaN multiple quantum well (MQW) structures, a novel defect (called the “V-defect”) initiates at threading dislocations in one of the first quantum wells in a MQW stack. This defect is common to almost all InGaN MQW heterostructures. The nature of the V-defect was evaluated using transmission electron microscopy (TEM), scanning TEM (STEM), and low-temperature cathodoluminescence (CL) on a series of In0.20Ga0.80N/GaN MQW samples. The structure of the V-defect includes buried side-wall quantum wells (on the {1011} planes) and an open hexagonal inverted pyramid which is defined by the six {1011} planes. Thus, in cross section this defect appears as an open “V”. The formation of the V-defect is kinetically controlled by reduced Ga incorporation on the pyramid walls ({1011} planes). The V-defect is correlated with the localized excitonic recombination centers that give rise to a long-wavelength shoulder in photoluminescence (PL) and CL spectra. This long-wavelength shoulder has the fol...

DEPOSITION OF THREE-DIMENSIONAL GE ISLANDS ON SI(001) BY CHEMICAL VAPOR DEPOSITION AT ATMOSPHERIC AND REDUCED PRESSURES

This report summarizes observations of Ge island formation during growth on Si(001) by chemical vapor deposition from germane in the pressure range from 10 Torr to atmospheric pressure in a conventional epitaxial reactor. A four-step growth process is observed: (1) uniform pseudomorphic overlayer (“wetting’’ layer) formation; (2) three-dimensional island growth with a constant aspect ratio; (3) continued island growth with a constant diameter and increasing height; (4) rapid growth of larger, faceted islands. Ostwald ripening of the islands during continued heat treatment after terminating the deposition is slow compared to island formation and growth during deposition for the experimental conditions used.

Structural and optical properties of GaN laterally overgrown on Si(111) by metalorganic chemical vapor deposition using an AlN buffer layer

Lateral epitaxial overgrowth (LEO) on Si(111) substrates using an AlN buffer layer is demonstrated and characterized using scanning electron microscopy, atomic force microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence spectroscopy, and cathodoluminescence imaging. The 00>-oriented LEO GaN stripes grown on silicon substrates are shown to have similar structural properties as LEO GaN grown on GaN/Al 2 O 3 substrates: the surface topography is characterized by continuous crystallographic steps rather than by steps terminated by screw-component threading dislocations; the density of threading dislocations is 6 cm −2 ; the LEO regions exhibit crystallographic tilt (0.7-4.7°) relative to the seed region. The AlN buffer thickness affects the stripe morphology and, in turn, the microstructure of the LEO GaN. The issues of chemical compability and thermal expansion mismatch are discussed.

Cathodoluminescence mapping of epitaxial lateral overgrowth in gallium nitride

The dislocation arrangements in gallium nitride (GaN) films prepared by lateral epitaxial overgrowth (LEO) have been studied by cathodoluminescence mapping and transmission electron microscopy. A very low density of electrically active defects (<10−6 cm−2) in the laterally overgrown material is observed. Individual electrically active defects have been observed that propagate laterally from the line of stripe coalescence into the overgrown material. Additionally, by mapping wavelength-resolved luminescence in an InGaN quantum well grown on top of the overgrown material, these defects are shown to be limited to the underlying material and do not propagate normal to the surface, as in other GaN films. In the seed region, threading dislocation image widths are seen to be nearly identical in the quantum well and the underlying GaN, indicating a comparable upper limit (∼200 nm) for minority carrier diffusion length in InGaN and GaN. Additionally, it is shown that, through processing variation, these lateral de...

Low‐resistance Ohmic conduction across compound semiconductor wafer‐bonded interfaces

Data are presented demonstrating low‐resistance Ohmic conduction across interfaces formed by high‐temperature (750–1000 °C) compound semiconductor wafer bonding. Unipolar junctions formed by wafer bonding surfaces consisting of In0.5Ga0.5P/In0.5Ga0.5P, GaP/GaP, GaP/In0.5Ga0.5P, and In0.5Ga0.5P/GaAs are shown to exhibit low‐resistance Ohmic conduction for both p‐ and n‐isotype junctions. The achievement of these properties is demonstrated to be critically dependent upon the crystallographic alignment of the bonded wafer surfaces, irrespective of the lattice mismatch between the surfaces. Specifically, we show that the surface orientation of the bonded surfaces must be nominally matched while simultaneously maintaining rotational alignment of the wafers.

Limited reaction processing: Growth of Si1−xGex/Si for heterojunction bipolar transistor applications

Abstract Limited reaction processing (LRP) of silicon-based materials is reviewed as an alternative growth method to molecular beam epitaxy (MBE). LRP is a chemical vapor deposition technique which uses wafer temperature, rather than gas flow switching, to initiate and terminate growth. Processing takes place within a cold-wall, quartz reaction chamber, and gases are changed between successive lamp-heated growth cycles. In addition to minimizing thermal exposure, the technique allows individual layers in a multi-layer structure to be deposited at their optimum growth temperature. LRP is particularly well suited to the growth and processing of metastable layers such as strained Si 1− x Ge x on silicon. Several properties of LRP-grown Si 1− x Ge x are shown to be similar to those reported for MBE material, including qualitative islanding behavior and quantitative measurement of the onset of misfit dislocation formation. However, a direct comparison of thermal stability reveals larger numbers of misfit dislocations in MBE-grown films upon annealing. The electrical behavior of misfit dislocations in heterojunction diodes, and the growth and analysis of high-quality Si/Si 1− x Ge x /Si heterojunction bipolar transistors are also discussed.

Unusual properties of photoluminescence from partially ordered Ga0.5In0.5P

Ga0.5In0.5P grown lattice matched to GaAs by metalorganic chemical vapor deposition (MOCVD) exhibited domains of varying degrees of column III sublattice ordering. Continuous‐wave photoluminescence spectra were single peaked and relatively narrow, but the peak wavelengths from samples grown at low (630–670 °C) temperatures varied strongly with excitation density at low measurement temperatures, while peak wavelength did not vary for high (775 °C) temperature growth. The half width was 6.5 meV in the latter case, the narrowest reported from MOCVD‐grown Ga0.5In0.5P. Time‐resolved photoluminescence of partially ordered GaInP at liquid‐helium temperatures is reported for the first time. For samples grown at low temperatures, the spectral peak displayed a slow (τ≳1 μs) decay at low excitation density. The decay was more rapid (τ=1.8 ns) at higher excitations and at higher photon emission energies. Possible explanations discussed include spatial separation of carriers and trapping.

A high-speed bipolar technology featuring self-aligned single-poly base and submicrometer emitter contacts

An experimental bipolar transistor structure with self-aligned base-emitter contacts formed using one polysilicon layer is presented with geometries and frequency performance comparable to those of double-polysilicon structures. This structure, called STRIPE (self-aligned trench-isolated polysilicon electrodes), provides a 0.2- mu m emitter-base polysilicon contact separation. A 0.4- mu m emitter width is achieved with conventional 0.8- mu m optical lithography. Scaling of the emitter width of 0.3 mu m has been performed with minimal degradation of device performance, and scaling of the emitter width pattern to 0.2 mu m has been demonstrated. These dimensions are the smallest achieved in single-polysilicon structures with polysilicon base contacts and are comparable to those achieved in double-polysilicon structures. The STRIPE structure has been used to fabricate transistors with f/sub t/ as high as 33.8 GHz.<<ETX>>

Effect of substrate surface structure on nucleation of GaAs on Si(100)

We study the effect of surface structure upon the nucleation of GaAs in molecular beam epitaxy growth on vicinal Si(100) surfaces. In general, cross‐sectional transmission electron microscopy reveals that nucleation of GaAs islands is associated with surface steps produced by the deliberate substrate misorientation. Furthermore, it is found that standard in situ cleaning of the Si surface prior to deposition can result in steps grouping together, producing local surface facets. GaAs nucleation then occurs on these facets, the nucleation sites being correspondingly further apart than for an equilibrium distribution of monolayer steps.