Npn AlGaN/GaN heterojunction bipolar transistors and GaN bipolar junction transistors with regrown C-doped GaAs in the base regions

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Low resistance ohmic contacts are difficult to form on p-type GaN and AlGaN due to the relatively high ionization energy of Mg in GaN and AlGaN. A carbon-doped GaAs grown on p-GaN prior to ohmic metallization has been shown to improve contact resistance to p-GaN. npn AlGaN/GaN heterojunction bipolar transistors and GaN bipolar junction transistors have been demonstrated by employing a regrowth C-doped GaAs to the p-GaN base regions. GaN/AlGaN epilayers were grown with a molecular beam epitaxy system and C-doped GaAs (10 20 cm −3) was regrown on the devices (∼500 Å) by metal organic chemical vapor deposition using SiO 2 as mask. Very high current densities were achieved for common base operation in both device types and devices were operable at 250°C.