Effect of indium doping on the transient optical properties of GaN films

Abstract

We have investigated the effects of In doping on the optical properties of GaN films grown by gas-source molecular-beam epitaxy. Time-resolved photoluminescence was carried out to study the transient optical properties of the epitaxial films. In comparison to the undoped GaN film, the spontaneous emission lifetime was prolonged from below 20 to 70 ps by doping with In. Under high-excitation density, stimulated emission was observed from both samples. The threshold excitation density was found to be reduced in the In-doped sample. These significant improvements of the optical properties are attributed to the effective suppression of the formation of the nonradiative recombination centers caused by a change of the growth kinetics induced by a small amount of In supplied during growth of the GaN films. © 1999 American Institute of Physics. ͓S0003-6951͑99͒00345-9͔GaN and related III-V nitride materials have recently drawn a great deal of attention mainly because of their possible applications in light emitting devices operating in the green, blue, and ultraviolet wavelength regions. InGaN ternary alloys are widely used as the active layer for practical devices such as blue/green light-emitting diodes 1 and violet laser diodes. 2 A further extension to shorter wavelength requires the GaN or AlGaN as active layers. However, devices realized with these active layers are rare, partly because materials with wide band gaps energy easily suffer from the formation of nonradiative recombination centers which may lead to a deterioration in luminescence efficiency. A solution to this problem may be to use a surfactant. 3 Surfactants are expected to modify the kinetics of epitaxial growth, therefore choosing the adequate surfactant could result in the improvement of crystal quality by controlling the surface diffusion length of the adatoms. Recently, some experimental reports on In surfactant effects investigated from a viewpoint of optical, 4-6 electrical, 6 and growth properties 7 have been published. All those studies showed positive effects of In, supplied on the surfaces during growth, to improve the crystal quality of GaN.In this study, we demonstrate the effect of In doping on the improvement of crystal quality by performing timeresolved photoluminescence ͑TRPL͒ spectroscopy. Because the carrier lifetime reflects the concentration of recombination centers directly, this investigation method provided us with a sensitive probe for detection of nonradiative recombination centers. The excitation density was chosen in the range where the corresponding photogenerated carrier density was around and above the Mott density. This allowed us to explore the optical properties under a high carrier density similar to what is found in commercial devices operating under high carrier injection.In-doped GaN films as well as undoped films ͑both approximately 0.4 m thick͒ were prepared by gas-source molecular-beam epitaxy ͑GS-MBE͒ on low-temperature grown GaN buffer/Al 2 O 3 substrate. Details about the growth procedure can be found in Ref....

Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant

“…All these improvements are more significant for samples grown with nitrogen as a carrier gas, having higher dislocation density. This is consistent with the previously observed rather drastic improvements of properties for MBE-grown samples, 4,5 where the dislocation density is much higher.…”

Effect of Isoelectronic In Doping on Deep Levels in GaN Grown by MOCVD

“…Recently, it was found that isoelectronic In doping has definite effects of controlling the density of dislocations and improving the GaN film quality. Some experimental reports on the characteristics of In-doped GaN films investigated from a viewpoint of optical [6][7][8], electrical [9,10], and growth properties [11] have been published. However, there are few reports about the behavior of deep level defects with isoelectronic In doping.…”

Non-Monotonous Behavior of In-Doped GaN Grown by MOVPE with Nitrogen Carrier Gas

“…Indium is the most widely studied surfactant in the epitaxial growth of GaN. The improvement in the crystalline quality, electrical and optical properties, and surface morphology of the In-doped GaN have been reported for MOVPE [2][3][4][5] and MBE [6,7]. The roles of the In surfactant in the MOVPE growth of GaN are more significant when the N 2 carrier gas is used in comparison with the H 2 .…”