n-Type Diamond Growth by Phosphorus Doping

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n-Type Diamond Growth by Phosphorus Doping Hiromitsu Kato, Toshiharu Makino, Satoshi Yamasaki, and Hideyo Okushi Nanotechnology Research Institute, AIST, 1-1-1 umezono, Tsukuba, 305-8568, Japan ABSTRACT Phosphorus doping on (001)-oriented diamond is introduced and compared with results achieved on (111) diamond. Detailed procedures, conditions, doping characteristics, and recent electrical properties of (001) phosphorus-doped diamond films are described. Now the highest mobility is reached to be ~780 cm2/Vs at room temperature. The carrier compensation ratio, which is still high around 50-80 %, is the most important issues for (001) phosphorus-doped diamond to improve its electrical property. The origin of compensators in phosphorus-doped diamond is investigated, while yet to be identified. Ultraviolet light emitting diode with p-i-n junction structure is also introduced using (001) n-type diamond. A strong UV light emission at around ~240 nm is observed even at room temperature. High performance of diamond UV-LED is demonstrated. INTRODUCTION Diamond is expected to be a promising next-generation wide-band-gap semiconductor for electronic and optical applications, such as ultraviolet light emitting diodes (UV-LED), cold cathode electron emitters, DNA sensors, and high-power and high-frequency devices. Particularly, exciton-related devices and electron emitters with negative electron affinity are considered to be future applications utilizing the unique properties of diamond. To realize these applications, several fundamental technological issues must be resolved including high-quality diamond growth, p- or n-type doping, contact fabrication, and etching technology. Especially, ntype doping is still the most difficult task to optimize in diamond synthesis. Since the 1980s, which brought the introduction of chemical vapor deposition (CVD) of diamond using microwave plasmas [1], many studies have been carried out on intrinsic diamond growth and on p- or n-type doping by CVD. For p-type diamond, the impurity boron, B, is easily incorporated into both natural and synthetic diamond by CVD without any restriction on crystal orientation. The boron acceptor level was determined to be ~0.37 eV above the top of valence band. The quality of boron-doped CVD diamond has now reached a maximum mobility of ~1840 cm2/Vs at 290 K as determined by Hall-effect measurements [2], which is close to the maximum value of ~2010 cm2/Vs obtained for natural IIb crystals [3]. On the other hand, n-type diamond is not present in nature, and controlled n-type doping had been considered almost impossible until 1997. Among the group V elements, nitrogen was one of the candidates for ntype doping because of its similar covalent bond length (0.74 Å) to that of diamond (0.77 Å), but unfortunately, it forms a deep donor level at ~1.7 eV below the bottom of the conduction band, due to its structural distortion from the substitutional position in the diamond lattice [4]. Phosphorus, P, has long been considered as another candidate for n-type d