Charge carrier transport and electroluminescence in atomic layer deposited poly-GaN/c-Si heterojunction diodes

Abstract

In this work, we study the charge carrier transport and electroluminescence (EL) in thin-film polycrystalline (poly-) GaN/c-Si heterojunction diodes realized using a plasma enhanced atomic layer deposition process. The fabricated poly-GaN/p-Si diode with a native oxide at the interface showed a rectifying behavior (Ion/Ioff ratio ∼ 103 at ±3 V) with current-voltage characteristics reaching an ideality factor n of ∼5.17. The areal (Ja) and peripheral (Jp) components of the current density were extracted, and their temperature dependencies were studied. The space charge limited current (SCLC) in the presence of traps is identified as the dominant carrier transport mechanism for Ja in forward bias. An effective trap density of 4.6 × 1017/cm3 at a trap energy level of 0.13 eV below the GaN conduction band minimum was estimated by analyzing Ja. Other basic electrical properties of the material such as the free carrier concentration, effective density of states in the conduction band, electron mobility, and dielectric relaxation time were also determined from the current-voltage analysis in the SCLC regime. Further, infrared EL corresponding to the Si bandgap was observed from the fabricated diodes. The observed EL intensity from the GaN/p-Si heterojunction diode is ∼3 orders of magnitude higher as compared to the conventional Si only counterpart. The enhanced infrared light emission is attributed to the improved injector efficiency of the GaN/Si diode because of the wide bandgap of the poly-GaN layer and the resulting band discontinuity at the GaN/Si interface.