High gain bipolar photo-transistor operation in graphene/SiC Schottky interfaces: The role of minority carriers

Abstract

We propose a new class of semiconductor transistor devices based on graphene/SiC and graphene/Si Schottky junctions that have the potential to be transformative. By using the graphene as collector/emitter in a bipolar transistor (BJT) and not as a channel material, there is relaxation of the tolerances in graphene thickness and quality, simplifying growth, device design and fabrication. This also enables the exploitation of engineered defects in thicker (2-5ML) graphene films for flexible electronics, currently not being considered, as well controlled uniform defects are preferred to localized random defect clusters. We will discuss an SiF4 based growth method that enables temperature programmed defect engineering. We will discuss the use of electron-beam induced current (EBIC) to characterize these materials. Based on recent results at our lab, a graphene/SiC Schottky junction behaves as a collector (GC) and an emitter (GE) in a BJT with common emitter gain, β>50, measured under phototransistor operation mode. The transparent graphene Schottky collector/emitter junction enables opto-electronic applications, minimizes series resistance in the device due to the thin graphene layer, and also minimizes charge storage time (diffusion capacitance), enabling high speed operation. Furthermore, the observation of β>50 with a GE-BJT demonstrates that significant minority carrier injection occurs in these Schottky junctions, contrary to what is commonly assumed. The injection of minority carriers has the ability to induce conductivity modulation in the underlying semiconductor, reducing overall device resistance. The role of minority carriers in Schottky Junctions will be discussed.