GaN/ZnO and AlGaN/ZnO heterostructure LEDs: growth, fabrication, optical and electrical characterization
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1201-H01-08
GaN/ZnO and AlGaN/ZnO heterostructure LEDs: growth, fabrication, optical and electrical characterization J. Benz1, S. Eisermann1, P. J. Klar1, B. K. Meyer1, T. Detchprohm2 and C. Wetzel2 I. Physikalisches Instiut, Justus-Liebig Universität, Heinrich-Buff-Ring 16, 35392 Giessen, Germany 2 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180-3590, U.S.A. 1
ABSTRACT The wide bandgap polar semiconductors GaN and ZnO and their related alloys exhibit fascinating properties in terms of bandgap engineering, carrier confinement, internal polarisation fields, and surface terminations. With a small lattice mismatch of ~1.8 % between GaN and ZnO and the possibility to grow MgZnO lattice-matched to GaN, the system AlGaN/MgZnO offers the opportunity to design novel optoelectronic devices circumventing the problem of p-type doping of ZnO. In such AlGaN/MgZnO heterostructures with either hetero- or isovalent interfaces, tuning of band offsets is possible in various ways by polarisation fields, surface termination, strain, and composition. These aspects need to be fully understood to be able to make full use of this class of heterostructures. We report on the growth of ZnO films by chemical vapor deposition on p-type GaN and AlGaN grown by metal-organic vapor deposition on sapphire templates and on the fabrication of corresponding light-emitting diode (LED) structures. Electrical and optical properties of the n-ZnO/p-GaN and n-ZnO/p-AlGaN LEDs will be compared and the observed differences will be discussed in terms of the band alignment at the heterointerface. INTRODUCTION The wide bandgap semiconductor zinc oxide is a promising material for the production of blue and ultraviolet optoelectronic devices such as light emitting diodes (LEDs), laser diodes and photo diodes. Compared to GaN, the semiconductor mainly used in the optoelectronic industry for the production of short wavelength devices; ZnO offers several advantages, e.g. larger exciton binding energy (60 meV for ZnO versus 26 meV for GaN), which may lead to UV sources with higher brightness and lower power thresholds at room temperature. ZnO possesses higher radiation hardness than Si, GaAs, CdS and GaN, therefore it should be suitable for space applications. Last but not least, large area substrates of ZnO are available at relatively low material costs and ZnO offers a simplified processing, as it can be microstructured by conventional wet-chemical etching [1-4]. Despite all these advantages, there remains one obstacle to be overcome before reliable, entirely ZnO-based optoelectronic devices become reality: the problem of p-type doping of ZnO. So far, there is no way to reliably produce stable and high quality p-type ZnO. Considering the similarity of the physical properties of ZnO and GaN, which both crystallize in wurtzite structure with a lattice mismatch of ~1.8%, and the availability of high quality p-GaN, a natural way of circumventing the doping issue is to grow nMgZnO/p-AlGaN based d
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