Optical Spectroscopy of Ingan Epilayers in the Low Indium Composition Regime
- PDF / 66,944 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 210 Views
ABSTRACT Photoluminescence (PL) spectroscopy was carried out on a series of Si-doped bulk InGaN films in the low indium (In) composition regime. Room temperature PL
showed a factor of 25 increase in integrated intensity as the In composition was increased from 0 to 0.07. Temperature dependent PL data was fit to an Arrhenius equation to reveal an increasing activation energy for thermal quenching of the PL intensity as the In composition is increased. Time resolved PL measurements revealed that only the sample with highest In ( x=0.07) showed a strong spectral variation in decay time across the T=4K PL resonance, indicative of recombination from localized states at low temperatures. The decay times at room temperature were non-radiatively dominated for all films, and the room temperature (non-radiative) decay times increased with increasing In, from 50-230 psec for x=0-0.07. Our data demonstrate that non-radiative recombination is less effective with increasing In composition.
INTRODUCTION While a great deal of progress has been made in the development of InGaNbased light emitters, the role played by indium (In) in contributing to the optical efficiency is still quite controversial. A number of groups have proposed that the inhomogeneity of In incorporation results in carrier localization at In-rich regions and that this localization leads to enhanced optical efficiency [1-3]. Support of this hypothesis is found in cathodoluminescence experiments that demonstrate a variation of the PL emission energy on the microscale, suggesting that In composition variations on the order of several percent are possible [4]. Further insight is suggested by the timeresolved spectroscopy experiments of InGaN quantum well structures performed by Narukawa, et. al. [5], which suggest that the density of non-radiative centers and possibly the non-radiative recombination mechanism itself is altered when In is included in the growth. A similar result was obtained by Kumano, et. al. [6] who suggest that increased optical efficiency is due to reduced non-radiative recombination centers with In incorporation. These two phenomena, namely localization and reduced non-radiative recombination, may be linked if dislocations act as non-radiative centers [7,8], and if the presence of dislocations also affects the inhomogeneity of In incorporation [8,9], thereby affecting carrier localization. In contrast to these theories, other experiments [10] suggest that the majority of optical spectroscopy data on InGaN quantum wells can be explained entirely by piezoelectric field effects. Thus, it is clear that a strong consensus has not emerged as to whether localization is indeed the primary mechanism by which InGaN alloys and quantum wells achieve high optical efficiencies. In this paper, we explore these issues through an examination of the effect of In composition on the optical properties of InGaN alloys. Our studies include temperature-
F99W11.41
dependent and time-resolved photoluminescence spectroscopy measurements on a number of MOVPE growth In
Data Loading...
