Traps in Si-doped AlxGa1-xN Grown by Molecular Beam Epitaxy on Sapphire Characterized by Deep Level Transient Spectrosco
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Traps in Si-doped AlxGa1-xN Grown by Molecular Beam Epitaxy on Sapphire Characterized by Deep Level Transient Spectroscopy Mo Ahoujja1, S Elhamri1, M Hogsed2, Y. K. Yeo2, and R. L. Hengehold2 1 Physics, University of Dayton, 300 College Park, Dayton, OH, 45469 2 ENP, AFIT, WPAFB, Dayton, OH, 45433 ABSTRACT Deep levels in Si doped AlxGa1-xN samples, with Al mole fraction in the range of x = 0 to 0.30, grown by radio-frequency plasma activated molecular beam epitaxy on sapphire substrates were characterized by deep level transient spectroscopy (DLTS). DLTS measurements show two significant electron traps, P1 and P2, in AlGaN at all aluminum mole fractions. The electron trap, P2, appears to be a superposition of traps A and B , both of which are observed in GaN grown by various growth techniques and are thought to be related to VGa-shallow donor complexes. Trap P1 is related to line defects and N-related point defects. Both of these traps are distributed throughout the bulk of the epitaxial layer. An additional trap P0 which was observed in Al0.20Ga0.80N and Al0.30Ga0.70N is of unknown origin, but like P1 and P2, it exhibits dislocation-related capture kinetics. The activation energy measured from the conduction band of the defects is found to increase with Al mole content, a behavior consistent with other III-V semiconductors. INTRODUCTION AlxGa1-xN materials are of interest in the fabrication of high-temperature and highfrequency electronic devices, as well as blue to UV light emitting and detecting devices. Devices based on AlxGa1-xN layers include bipolar junction transistors [1], solar blind photodiodes [2], and high electron mobility AlGaN/GaN heterostructures [3]. Despite the considerable effort concentrated on the fabrication of nitride based devices, there have been relatively few studies on the growth and characterization of AlxGa1-xN alloys [4, 5]. Defects and impurities, which are either intentionally or unintentionally introduced, often control the properties of these materials and are responsible for the degradation of device performance [6]. Therefore, an understanding of the role of the extended, and point defects in AlxGa1-xN, and the mechanisms for their formation is essential for the realization of high performance devices. In this study, deep levels in Si doped AlxGa1-xN samples with Al mole fraction in the range of x = 0 to 0.30 grown by radio-frequency plasma activated molecular beam epitaxy are investigated using conventional DLTS measurements. EXPERIMENT Wafers of 1 µm thick AlxGa1-xN layers doped with silicon were grown by radiofrequency plasma assisted molecular beam epitaxy (MBE) on the c-plane of a sapphire substrate. Prior to metal deposition, the AlxGa1-xN wafers were cut into small pieces of 5x5 mm2 each, degreased using standard chemical solvents, and followed by a dip in a
boiling aqua regia (HCL / HNO3 : 3/1) solution for 30 s and a rinse in de-ionized water. For Ohmic contacts, a Ti(300Å)/Al(800Å)/Ti(1200Å) /Au(500Å) metallization was deposited by electron beam evaporat
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