Kendinden yerleşmeli galyum nitrit tabanlı iki kutuplu transistörlerin fabrikasyonu için potansiyel yardımlı foton katkılı elektrokimyasal aşındırma

GaN-based bipolar transistors are good candidates for applications in RF poweramplifiers. In contrast to more common AlGaN/GaN high electron mobilitytransistors (HEMTs), GaN based bipolar transistors have not drawn muchattention because of the difficulties in good p-type material and ohmic contact.Most of the problems associated with p-type quality and contact come fromgrowth and etch damage during fabrication.In this work, a low damage etching technique with an undercut profile wasdeveloped to solve the problems associated with p-type ohmic contact qualityand to realize the self-aligned GaN bipolar transistor fabrication. The etchingprocess consists of bias-assisted photoenhanced electrochemical oxidation ofGaN in deionized water (BPECO/DI) and its subsequent etching in diluted acidsolution. By this technique, we demonstrated good Schottky contacts on samplesetched more than 100 nm and p/n doping selective etching was shown.Furthermore the most critical point for self-aligned fabrication is undercutprofile and it was also obtained by BPECO/DI etching. Hence this technique isideal for fabrication of self-aligned bipolar transistors.There are some problems during fabrication of self-aligned bipolar transistor.First, due to the impossibility of activation annealing after emitter etch,activation annealing had to be done at the beginning where emitter layer is onthe base and this was a problem for Mg activation. More importantly, there werestill uncertainties with BPECO/DI etching like roughening up the etchedsurface, low etch rate for npn structures and disturbing the material uniformitynear the surface.In this work, it was shown that BPECO/DI etching is a very efficient tool thatprovided low damage etching of GaN and enabled the self aligned RF bipolartransistor structures. It was found that self aligned base-emitter junctions weresuccessfully formed and the BPECO/DI etching was almost stopped at top of thebase layer. Self-aligned bipolar transistors were fabricated and their base-emitterand base-collector junctions were measured. The results obtained in this workdemonstrated that BPECO/DI etching can bring solutions to the lack of lowdamage etching and the impossibility of self-aligned base contact in fabricationof today's GaN based bipolar transistors.Keywords: Gallium nitride, bipolar transistor, photo-enhanced electrochemicaletching, low damage etching, self-aligned process