Effect of threading dislocations on AlGaN/GaN heterojunction bipolar transistors

We demonstrate an AlGaN/GaN heterojunction bipolar transistor on a substrat e grown using the lateral epitaxial overgrowth (LEO) technique. Common emit ter characteristics show a current gain of 3. Active layers were grown by p lasma-assisted molecular-beam epitaxy on metal-organic chemical-vapor-depos ition-grown templates on sapphire. The collector-emitter leakage mechanism in these devices is found to be local punch-through associated with base la yer compensation near the dislocations. LEO wing regions (nondislocated) we re found to reduce the emitter-collector leakage by four orders of magnitud e over adjacent window regions which had a dislocation density of 10(8) cm( -2). Varying the doping profile through the base confirms that the mechanis m for leakage is local punch-through due to compensation. This compensation mechanism is consistent with simulations which assume a donor-state line d ensity of 10(7) cm(-1). The implications of the emitter-collector leakage f or dc device characterization are also discussed. (C) 2001 American Institu te of Physics.