Wafer fused AlGaAs/GaAs/GaN HBTs with current gain of ~ 20 and fT of ~ 2.6 GHz

Wafer fusion is a powerful technique in integrating heterogeneous materials. The most well known example is silicon-on-insulator (SOI), and the more recent success is the hybrid silicon laser. Most often the fused interface is incorporated in a device structure where its electronic properties are not crucial to the device performance, considering this interface is normally more defective than epitaxial growth interfaces or thermal oxidation interfaces. However, Levine et al. (1997). demonstrated 20 GHz operation of planar Si/InGaAs p-i-n photodetectors with very low dark current using wafer fusion, suggesting that a fusion interface may be of high quality and situated in the device active region. To this end, we have explored the double heterojunction AlGaAs/GaAs/GaN bipolar transistor using wafer fusion, which are otherwise difficult to grow epitaxially. This device structure takes advantage of the superior p-type doping and transport properties of the (Al)GaAs material system and the high breakdown voltage in GaN, which could be promising for high-speed high-power applications. We report here the DC performance of these devices upon optimizing wafer fusion conditions and the performance of the RF devices, which have been realized for the first time.