High P-Type Gan For Advanced Optoelectronic Devices

III-nitride semiconductors are well-suited for solid-state lightening, such as light-emitting diodes (LEDs) and laser diodes (LDs). GaN (3.4 eV) alloyed with InN (0.7 eV) and AlN (6.1 eV) can cover a continuous range of a direct band-gap energy. A wide spectrum range from red to deep ultra-violet has been achieved using III-nitride LEDs 12 . Advanced optoelectronic devices demand higher power output and lower energy consumption. Conventional GaN-based optoelectronic devices suffer from rather high p-type contact resistance in the mid-10 −4 Ωcm 2 , leading to high threshold voltage for high current optoelectronic devices. Generally, Mg is used as p-type dopant of GaN. Mg-doped GaN (GaN:Mg) has an intrinsically low ionized-acceptor concentration (10 17 -10 18 cm −3 ) due to the large ionization energy Ea of Mg (∼0.18 eV) and high compensation by donor-like defects such as nitrogen vacancy. Mg doping level beyond ∼10 20 cm −3 causes generation of V-shaped pyramidal extended defects into GaN layers and polarity inversion of their wurtzite crystal structure. These low effective-acceptor concentrations (N a -N d ) prevent ptype contact resistance from decreasing through field-emission (FE) tunneling. Recently, the formation of compensation defects in GaN:Mg was hindered thanks to the low growth temperature of 740 °C by molecular-beam epitaxy (MBE) using ammonia gas. This allows achieving high acceptor concentrations over 10 19 cm −3 3 4 . Here we report on the electrical properties of heavily Mg-doped GaN and carry out systematic investigation of p-type contact resistance.