Deep centers and their spatial distribution in undoped GaN films grown by organometallic vapor phase epitaxy

Abstract

Deep traps in undoped n-GaN layers grown by organometallic vapor phase epitaxy on sapphire substrates were studied by temperature dependent conductivity, photoinduced current transient spectroscopy (PICTS), thermally stimulated current, electron beam induced current (EBIC), and band edge cathodoluminescence (CL) methods. Presence of electron traps with energy levels 0.1–0.2 eV below the conduction band and hole traps with energy levels of about 0.25, 0.5, and 0.85 eV above the valence band edge was detected. CL and EBIC measurements show that the deep recombination centers in GaN are distributed inhomogeneously with well defined cellular pattern. Both carrier lifetime and luminescence intensity are enhanced at cell walls indicating lower density of recombination centers. However, the density of main hole trap (0.85 eV) is enhanced in these regions as determined by local PICTS measurements. Photoconductivity in many GaN samples exhibits very long decay times at temperatures between 100 and 300 K. The effect most probably is not related to shallow donors such as silicon, but rather is associated with unidentified deep centers with a 0.2 eV barrier for electron capture.

Deep electron and hole traps in freestanding n-GaN grown by hydride vapor phase epitaxy

“…and densities of residual donors and acceptors as low as 7 ϫ10 15 and 2ϫ10 15 cm Ϫ3 , respectively. 4,5 Studying such crystals is also very interesting from a purely scientific viewpoint because it provides access to reasonably low dislocation density material which makes it possible to separately study the impact of point defects and dislocations on the electrical and recombination properties of n-GaN.…”

Neutron Radiation Effects in Epitaxially Laterally Overgrown GaN Films

“…The dominant hole traps in the virgin samples were the well-known E v +0.9 eV hole traps commonly observed in undoped n-GaN films. 23,24 The signal from these traps decreased with neutron dose, because of the decreasing lifetime of minority carriers. A broad hole-trap feature, absent in the virgin sample, emerged after Fig.…”

“…[20][21][22] For deep trap parameters in heavily compensated irradiated samples we used photo-induced current transient spectroscopy (PICTS). 23,24 Fast reactor neutron irradiation was performed in a WWR-c type reactor with doses of 10 13 to 10 18 cm -2 neutrons. Thermal neutrons in these experiments were filtered out by Cd foil; the temperature of the samples during irradiation did not exceed 30°C.…”

Current limitation after pinch-off in AlGaN/GaN FETs

“…The physical origin of the current reduction after pinch-off and its relation to the PPC is not yet understood. Further work has to be done to determine if the extracted activation energy E a is related to a discrete state or an emission barrier [5] [6] [7] [8]. The assumption that the PPC and the current reduction are of the same origin is under current investigation.…”