| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
O5, Time-Resolved Photoluminescence of AlInN/AlN Multiple Quantum Well Active Regions for Mid-UV Emitters |
| Author(s) |
Gregory A. Garrett, Hongen Shen, Michael Wraback, Hee Jin Kim, Zachary Lochner, Jae-Hyun Ryou, Russell D. Dupuis |
| On-Site Speaker (Planned) |
Gregory A. Garrett |
| Abstract Scope |
AlInN/AlN multiple quantum wells (MQWs) offer the possibility of reduced polarization fields and may provide opportunities for improved radiative efficiency through carrier localization relative to their more commonly employed AlGaN/Al(Ga)N counterparts. In this paper we present time-integrated and time-resolved photoluminescence (TRPL) studies of AlInN/AlN MQWs. The sample studied consisted of four AlInN QWs, 2 nm thick, with 2 nm AlN barriers and cap. This was on a 1 µm thick AlN buffer layer all grown by low pressure metalorganic chemical vapor deposition (MOCVD) on a c-plane sapphire substrate. Indium composition in the AlInN well was estimated to be 12% by high resolution x-ray diffraction. Temperature dependent TRPL was taken using a time-correlated single photon counting technique with 25 ps resolution. The excitation pulse source was a quadrupled Ti:Sapphire at 199.5 nm, allowing for increased carrier density through absorption in the AlN barriers. The excitation fluence ranged from ~0.75 to 100 µJ/cm<sup>2</sup>. Photoluminescence scans showed a peak at 276.7 nm at 13 K that shifted to 280.8 nm at 166 K while the intensity saturated and became sub-linear at high pump-powers. From 166 K to 300 K the PL shifted back toward 278 nm while becoming super-linear in intensity at all powers. At high fluence the peak was seen to blue-shift at all temperatures. A substantial low energy tail was also seen. The observation that the blue-shift with increasing fluence does not lead to a superlinear increase in PL emission at low temperature suggests a minimal electric-field contribution to emission from the deep and narrow wells, as carrier-induced screening of the polarization field should lead to enhanced wave function overlap and an improved radiative recombination rate. Rather, the blue-shift and sublinear PL emission intensity with increasing pump power imply band-filling of localized states in the wells, with a potentially reduced radiative recombination rate associated with delocalization of carriers at high pump power. The transition from sub- to super-linear intensity with temperature increase from 166K to room temperature shows the dominance of non-radiative recombination involving saturation of trap states, as reflected by the approximated IQE of 3% taken from the ratio of the room- to low-temperature PL. TRPL scans were dominated by a pronounced stretched exponential decay that is often associated with emission from excitons localized in an ensemble of tail states. At room temperature, the stretched decay is still observed at longer times, but the initial decay time shrinks from 186 ps at low temperature to 92 ps at room temperature, consistent with the low IQE. These studies suggest that carrier localization in AlInN MQWs may have a more pronounced effect on radiative recombination than that observed in traditional AlGaN structures, providing an intriguing alternative for mid-UV devices incorporating bulk AlN. |
| Proceedings Inclusion? |
Undecided |