HVPE GaN with Low Concentration of Point Defects for Power Electronics

  • PDF / 1,021,896 Bytes
  • 6 Pages / 612 x 792 pts (letter) Page_size
  • 40 Downloads / 148 Views

DOWNLOAD

REPORT


HVPE GaN with Low Concentration of Point Defects for Power Electronics M. A. Reshchikov,1 J.D. McNamara,1 A. Usikov,2,3 H. Helava,2 and Yu. Makarov2 1

Department of Physics, Virginia Commonwealth University, Richmond, VA 23284, USA Nitride Crystals, Inc. 181E Industry Ct., Ste. B, Deer Park, NY 11729, USA 3 Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, 49 Kronverkskiy Ave., 197101 Saint Petersburg, Russia 2

ABSTRACT We have studied photoluminescence (PL) from undoped GaN films grown by HVPE technique on sapphire. Several defect-related PL bands are observed in the low-temperature PL spectrum. The concentrations of the defects responsible for these PL bands are determined from the dependence of PL intensity on excitation intensity. The RL band with a maximum at 1.8 eV is often the dominant PL band in HVPE GaN. It is caused by an unknown defect with the concentration of up to ~1017 cm-3. The concentrations of defects responsible for other defectrelated PL bands rarely exceed 1015 cm-3. INTRODUCTION GaN and its alloys with InN and AlN are key components which are currently used to produce blue LEDs and laser diodes. GaN is also very promising material for high-power electronics [1,2]. The hydride vapor phase epitaxy (HVPE) technique, which is currently used for the growth of thick GaN films or freestanding templates, has several advantages including a very low density of dislocations, lower cost of production as compared to molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) techniques, and a low concentration of point defects. Photoluminescence (PL) is a powerful tool for studying point defects in GaN. Many defects in this material remain unidentified and not well understood [3]. One of the main PL bands in our HVPE GaN is the red luminescence (RL) band with a maximum at 1.8 eV and a zero-phonon line at 2.36 eV [4]. The RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band. In highquality, bulk GaN, the dominant defect-related PL band is the green luminescence (GL) band with a maximum at about 2.4 eV [5-8]. This PL band can be easily recognized in time-resolved PL measurements due to its exponential decay even at low temperatures, with a characteristic lifetime of 1-2 μs [3]. We preliminarily attributed the GL band to transitions of electrons from the conduction band to the 0/+ level of the isolated CN defect [9]. The yellow luminescence (YL) band, related to transitions via the −/0 level of the same defect, has a maximum at 2.1-2.2 eV and can be observed only for some high-purity samples. In less pure GaN samples, the YL band is attributed to the CNON complex [9,10]. The blue luminescence (BL) band with a maximum at 2.9 eV appears in PL spectrum for some samples and is caused by electron transitions via the ZnGa acceptor [3]. Finally, the ultraviolet luminescence (UVL) band is commonly observed