Robert Averbeck

MBE Growth of (In)GaN for LED Applications

We report on essential aspects of the growth of InGaN / GaN p-n junctions by gas-source molecular beam epitaxy (MBE) and present the first blue and green electroluminescence from such structures grown entirely by MBE.n A study of the growth conditions for a GaN nucleation layer on sapphire and for the subsequent growth of undoped GaN points out the necessity for Ga-stabilized growth. Unintentionally doped GaN grown at 1 μm/h shows background doping levels below 1017 cm-3 and mobilities up to 320 cm2/Vsec (at 300K). Narrow photoluminescence with very low intensity in the yellow spectral range is observed. N- and p-type doping of GaN with Si and Mg yields layers with high mobilities (220 and 10 cm2/Vsec, respectively at 300K) at carrier densities typical for devices.n Although incorporation of Indium is strongly temperature-dependent, InGaN-layers with In-contents of over 40% are obtained routinely. The optical properties of our InGaN layers typically exhibit the commonly observed, broad deep level luminescence. Finally, we present electroluminescence in the visible spectral range up to 540 nm from InGaN / GaN double-heterojunctions.

Plasma preconditioning of sapphire substrate for GaN epitaxy

Abstract The crystalline quality of molecular beam epitaxy (MBE)-grown layers of GaN on sapphire strongly depends on the initial stage of film nucleation and growth. Thus, pre-conditioning of the substrate is of vital importance. In this study we use X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) to examine in situ the case for surface cleaning and nitridation of c -plane sapphire substrates upon annealing in UHV and exposure to radio frequency (rf) plasmas of hydrogen and nitrogen, respectively. We find that low temperature (200–300 °C) heat treatment in a hydrogen plasma offers effective removal of adventitious surface contaminants, contrary to annealing in vacuum. Moreover, our XPS data provide unambiguous evidence for formation of surface nitride upon heat treatment in nitrogen plasma at 300–700 °C, in agreement with conclusions inferred from reflection high energy electron diffraction (RHEED). The surface nitride is found to remain stable on subsequent exposure to atmosphere.

GaN-based LEDs grown by molecular beam epitaxy

We report on the growth of GaN, InGaN and GaN/InGaN/GaN pn- junctions grown on sapphire by RF-plasma assisted MBE. MBE allows us to grow high quality nitrides with growth rates around 1 micrometers /h at relatively low temperatures. Thereby p- type doping with Mg and the incorporation of In in InGaN are greatly facilitated. Device-typical n- and p-type doping levels yield room temperature mobilities of 220 cm2/Vs and 10 cm2/Vs, respectively. InGaN with In contents of more than 40 percent is readily achieved. LEDs fabricated from heterostructures with a 4 nm InGaN layer show bright blue or green electroluminescence depending on the In content. Various effects in the electroluminescence caused by fluctuations in the conduction and valence band will be discussed, the most striking one a reduction in linewidth with increasing temperature.

Temperature dependence of the minimum V/III ratio for the growth of InxGa1-xAs

We have quantitatively determined the minimum V/III ratios for the growth of In x Ga 1-x As (x=0, 0.1, 0.2 and 0.53) on GaAs and InP. Minimum As 4 fluxes were measured for a wide range of growth temperatures using a transition of the surface reconstruction. Their temperature dependence can be fitted very well by the typical curve for thermally activated behavior. We find that the basic reaction kinetics of As 4 with In x Ga 1-x As are the same as with GaAs. The activation energies for As desorption from In x Ga 1-x As and GaAs are found to be similar (1.9 and 2.1 eV, respectively) but the rates of As-desorption are much higher for In x Ga 1-x As

Blue and green electroluminescence from GaNInGaN heterostructures

Abstract GaN InGaN pn-junctions were grown by molecular beam epitaxy. Depending on the In content bright blue (470 nm) or green (513 nm) electroluminescence was observed at room temperature.