Effect of Ge mole fraction on current, voltage and electric field characteristics of high doping nanoscale Si1−xGex/Si p-n diode

Abstract

In this paper, we report the simulation of high doping nanoscale heterojunction diode, particularly Si1−xGex/Si p-n diode, using Cogenda Visual TCAD. In order to gain knowledge on electrical properties of this diode, we exhaustively simulate the effect of Ge mole fraction in SiGe material on current, voltage and electric field characteristics. The simulation covers Ge mole fraction of 0.2 to 0.7 in SiGe material as acceptor and Si material as donor. Both acceptor and donor have concentrations of 10²⁰ per cm³ and areas of 10 × 10 nm². Under forward bias voltage, higher Ge mole fraction will produce higher current. This phenomenon happens due to lower energy band gap at higher Ge mole fraction condition. Besides that, higher Ge mole fraction has lower energy difference between P side and N side of diode. According to the simulation result, Si0.8Ge0.2 has energy band gap about 0.8 eV, meanwhile Si0.3Ge0.7 has energy band gap about 0.5 eV. Lower energy band gap causes more electrons have enough energy to cross the junction. Meanwhile under reverse bias voltage, high doping nanoscale diode will produce infinitesimal current. At the junction, high doping nanoscale Si1−xGex/Si P-N diode also has lower electric field (measured at the center of diode) at higher Ge mole fraction. Under reverse bias voltage of −2 V, Si0.3Ge0.7 has maximum electric field about 5.89 × 10⁶ V/m, meanwhile Si0.8Ge0.2 has maximum electric field about 6.17 × 10⁶ V/m. We predict that Ge mole fraction has inversely proportional effect to the maximum electric field value. Therefore, we concluded that Ge mole fraction affects current, voltage and electric field characteristics of high doping nanoscale Si1−xGex/Si P-N diode.