Doping of GaN by Ion Implantation: Does it Work?
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"Department of Physics & Astronomy, University of North Carolina, Chapel Hill, NC 27599 "*Metals and Seramics Division, Oak Ridge National Laboratory, Oak Ridge,,TN 37831-6376 "Departmentof Chemistry, University of North Carolina, Chapel Hill, NC 27599 Department of Materials Science & Engineering, NC State University, Raleigh, NC 27695 ** Implant *** Center, San-Jose, CA 95131 ABSTRACT Epitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si+ (for n-type) and 80 keV Mg+ (for p-type) with various fluences from lxlO12 to 7x10' 5 ions/cm 2 at liquid nitrogen temperature (LT), room temperature (RT), and 700 °C (HT). High temperature (1200 0C and 1500 °C) annealing was carried out after capping the GaN with epitaxial AIN by MOCVD to study damage recovery. Samples were capped by a layer of AIN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 °C decrease the lattice disorder; "hot implants" above 550 °C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg+ (5x 1014 cm 2) implanted and annealed GaN showed two peaks : one -100 meV and another -140 meV away from the band edge. INTRODUCTION In recent years attention to GaN related materials have risen because of potential and present applications, such as blue and ultraviolet light emitting diodes [1,2], blue lasers [3], UV detectors [4] and high-power and high-temperature FETs [5]. Regardless of the great success in the fabrication of optoelectronic and electronic devices, group III-nitrides suffer from difficulties in exhibiting the desired n- and p- type conduction [6-9]. Successful doping of GaN by ion implantation would be advantageous for device fabrication and therefore recovery of the implantation induced damage needs to be studied. So far there have been studies on ion damage generation and its partial recovery [10,11]. Additional studies are necessary to address the problem of effective doping of GaN by ion implantation. In this work we have performed implantations of Si+ and Mg+ in highly resistive epitaxially deposited GaN. Magnesium was chosen as the acceptor having low reported ionization energy, -160 meV [12]. Silicon was chosen as potential n- type dopant with reported ionization level 30 - 65 meV [13,14]. Implantations of silicon and magnesium were carried out at energies so that projected range of dopants would be -70 rn from the GaN surface. Implanted samples were capped by a layer of AIN grown epitaxially at 1000 °C by MOCVD. Subsequently, samples were annealed at
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