Origins of Parasitic Emissions from 353 nm AlGaN-based UV LEDs over SiC Substrates
- PDF / 162,455 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 226 Views
0892-FF09-02.1
Origins of Parasitic Emissions from 353 nm AlGaN-based UV LEDs over SiC Substrates Ji-Soo Park, D. W. Fothergill1, P. Wellenius1, S. M. Bishop, J. F. Muth1 and R. F. Davis Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907, USA 1 Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911, USA ABSTRACT The effects of p-GaN capping layers and p-type carrier-blocking layers on the occurrence of parasitic emissions from 353 nm AlGaN-based LEDs have been investigated. LEDs without a ptype Al0.25Ga0.75N carrier-blocking layer showed a shoulder peak at ~370 nm due to electron overflow into the p-Al0.10Ga0.90N cladding layer and subsequent electron-hole recombination in the acceptor levels. Broad emission between 380 and 450 nm from LEDs having a p-GaN capping layer was caused by 420 nm luminescence from the p-GaN capping layer, which was optically pumped by 353 nm UV emission from the quantum wells. Broad, defect-related luminescence at ~520 nm was emitted from the AlGaN layers within the quantum wells.
INTRODUCTION Substantial progress has been achieved in III-nitride based UV light emitting diodes (LEDs), due to their importance for applications including solid-state lighting and biochemical detection. UV LEDs having a wavelength range below 360 nm are fabricated using Al(In)GaN alloys. Longer wavelength parasitic emissions have been reported to often accompany the primary UV emissions. Adivarahan et al. reported that the principal 250 nm emission from AlGaN LEDs also contained broad visible emission at ~ 500 nm, due to deep level transitions from electron overflow into the p-AlGaN layers [1]. Shatalov et al. reported that 330 nm transitions to deep acceptor levels in p-AlGaN layers significantly influenced the LED internal quantum efficiency in 285 nm LEDs [2]. Hanlon et al. reported a shoulder peak at 360 nm in 292 nm LEDs, which supposedly corresponded to absorption and re-emission from the p-GaN capping layer [3]. Otuska et al. assumed that the broad peaks observed at ~ 400 and ~500 nm were due to nitrogen vacancies and a buffer layer, respectively, in their 339 nm LEDs [4]. And Chen et al. suggested that long wavelength emission at 373 nm may be caused by absorption and re-emission of the MQWs emission at 363 nm in the underlying n-GaN layers [5]. There have been few studies regarding the origins of parasitic emissions from UV LEDs. In this research, we fabricated 353 nm AlGaN-based UV LEDs and investigated the effect of the p-type GaN capping layer and the p-type AlGaN carrier-blocking layer (P-CBL) on the observed parasitic emissions. The origins of each parasitic emission were investigated using optical characterization of several LED structures and cathodoluminescence (CL) at different energies. EXPERIMENTAL DETAILS A schematic of the cross-section of the basic LED material structure grown in this research is shown in Figure 1. Detailed studies conducted to determine the optimum growth
0892-FF
Data Loading...
