Cost Effective Fabrication and Current-Voltage Characteristics of ZnO Homojunction Based n-p-n Bipolar Junction Transistor

This is the first report on successful fabrication of ZnO homojunction based n-p-n bipolar junction transistor (BJT) employing an easy cost-effective route and exploring its DC current (I)–voltage (V) characteristics, in all the three modes (common base, common emitter and common collector). Sol-gel grown undoped n-type layers was used to form emitter and collector regions; while the base was constituted of Sodium (Na) doped sol-gel grown p-type layer. The carrier concentrations of the emitter ( $2.2\times 10^{{18}}$ cm−3), base ( $1.35\times 10^{{16}}$ cm−3) and collector ( $2.58\times 10^{{17}}$ cm−3) were tuned by precisely tailoring the molarity of the precursor and the dopant concentrations. The doping/carrier concentration profile of emitter, base and collector was authenticated through EIS measurement. After carrying out the input and output I-V characteristics, DC current gain of the fabricated transistor were found to be 0.958 ( $\alpha {)}$ for common base, 24 ( $\beta {)}$ for common emitter and 24.6 ( $\gamma {)}$ for common collector mode, respectively. However, defects (due to vacancies and interstitials), and surface states were found to play the pivotal role (rather than bulk) in determining the leakage current (high) which eventually limits the gain.