NiIn as an Ohmic Contact to P-GaN

Abstract

ABSRTACTBased on the criteria for the solid state exchange reaction with p-GaN, we have investigated the intermetallic compound NiIn as a possible ohmic contact. The contacts were fabricated by depositing NiIn on p-GaN films (p ~ 2 x 10 17 cm -3 ) using RF sputtering from a compound target. The as-deposited, NiIn contacts were found to be rectifying and using I-V characterization a Schottky barrier height of 0.82 eV was measured. Rapid thermal annealing of the contacts was shown to significantly decrease their resistance, with contacts annealed at 800°C for 1 min yielding the lowest resistance. When annealed at 800 °C for 1 min NiIn contacts exhibited a specific contact resistance of 8-9 x 10 -3 Ω cm 2 , as measured by the circular transmission line model. To allow a more universal comparison the more traditional Ni/Au contacts, processed under the same conditions, were used as a standard. Their measured specific contact resistance (ρ c = 1.2 -2.1 x 10 -2 Ω cm 2 ) was significantly higher than that of the NiIn contacts. Demonstrating that NiIn has promise as an ohmic contact to p-GaN and should be studied in greater detail. INTRODUCTIONIt has long been realized that the III-V nitrides have tremendous potential for optoelectronic devices operating in the blue and UV wavelengths as well as for use in high power-high temperature semiconductor devices. The III-V nitrides form a continuous alloy system whose direct band gap ranges from 6.2 eV (AlN) to 3.4 eV (GaN) to 1.9 eV (InN) at room temperature.1 This potentially allows the fabrication of high efficiency optical devices, such as Light Emitting Diodes (LEDs), which can operate from orange to the UV region. The extension into the green and blue wavelengths completes the visible spectrum allowing semiconductor technology to be used for applications such as large full color displays and traffic lights. 2,3Early research into the nitrides outlined several problem areas, which hindered efforts to produce devices based on III-V nitride technology. Particularly the lack of p-GaN made the fabrication of efficient optical devices based on p-n junctions impossible, though some LEDs based on metal-insulator-semiconductors were fabricated. 1,3 Only recently due to advances in ptype doping has GaN started to realize its potential and there are now nitride based devices available. However, the metal contact to p-GaN is an important concern since high contact resistance will substantially reduce the performance of GaN based devices. In fact, the high resistance of the metal/p-GaN contact is one of the most significant issues limiting laser diode performance.Most of the current work on finding low resistance metallizations to p-GaN has focused on high work function elemental metals deposited in multilayer structures. [4][5][6][7][8][9][10][11] This strategy is based on the Schottky model, which predicts that higher work function metals will result in lower Schottky barriers to p-type semiconductors. on metal/p-GaN contacts suggests that the Schottky model is at least partially a...