Electrical properties and carrier transport mechanisms of n-ZnO/SiO_x/n-Si isotype heterojunctions with native or thermal oxide interlayers

Abstract

N-type ZnO/SiOx/n-type crystalline silicon isotype heterojunctions (HJs) have been prepared by magnetron sputtering. Native and thermal oxides were employed as the interlayer between the Si substrate and the ZnO film. Transmission electron microscopy and x-ray photoelectron spectroscopy revealed that an oxide layer was inserted in the HJ interface, with thickness of ∼1.2 nm (native oxide) and ∼2.0 nm (thermal oxide). Atomic force microscopy and x-ray diffraction spectroscopy showed that the ZnO film on the Si substrate consists of tightly packed grains with sizes in the range 50–150 nm and is c-axis preferred orientation. The electrical properties were characterized by current–voltage (I–V), capacitance–voltage (C–V) and current–voltage–temperature (I–V–T) measurements. By a comparison of the HJ properties, the n-ZnO/thermal oxide/n-Si HJs show improved electrical properties, with a fairly low leakage current and high rectification ratio, although the series resistance increased. Studies of fitting the I–V–T measurement data suggest that the tunnelling process is a dominant current transport mechanism for the n-ZnO/native or thermal oxide/n-Si HJs at an intermediate voltage range.

Mechanism of Carrier Transport at Low Temperatures in n-Type Beta-FeSi2/p-Type Si Heterojunctions Fabricated by Facing-Target Direct-Current Sputtering

“…(1), the ideality factor was estimated from the slope of the linear part from the forward lnJ-V characteristic curves using the relation: n =  Figure 3displays the temperature dependence of the ideality factor analyzed from the forward lnJ-V characteristic curves. At 300 K, the ideality factor was 1.23 and increased to 2.02 at 225 K. Ideality factor values  2 implied that the mechanism of carrier transport was governed by a recombination process in the β-FeSi2 layer and at the hetero junction interface [8].The defects in the β-FeSi2 layer might form a deep energy level in the band gap, which could act as a recombination center. At 200 K, the ideality factor was 3.34 and increased to 15.56 at 50 K. Ideality factor values >2implied that the tunneling process contributed to the mechanism of carrier transport [8].…”

“…At 300 K, the ideality factor was 1.23 and increased to 2.02 at 225 K. Ideality factor values  2 implied that the mechanism of carrier transport was governed by a recombination process in the β-FeSi2 layer and at the hetero junction interface [8].The defects in the β-FeSi2 layer might form a deep energy level in the band gap, which could act as a recombination center. At 200 K, the ideality factor was 3.34 and increased to 15.56 at 50 K. Ideality factor values >2implied that the tunneling process contributed to the mechanism of carrier transport [8]. This should be attributed to the existence of interface states at the junction interface and the localized electronic states in the β-FeSi2 layer.…”

“…To determine the mechanism of carrier transport in the hetero junctions, the J-V relationship is written as [6,8]:…”

Surface passivation of AZOY/n-Si interface of heterojunction solar cells with NH4F solution treatment

“…Therefore, the higher sheet resistance and lower work function of undoped ZnO thin films have been the main problems affecting FF (0.56) and V oc (410 mV), leading to a lower conversion efficiency for ZnO/n-Si than for ITO/n-Si HJSCs. Thus, to overcome the disadvantages of ZnO films, Al-doped ZnO (AZO) thin films have been widely used as an emitter layer in Si-based HJSC solar cell applications [11][12][13][14].…”

Effect of sputtering power on the performance of p-Ni1−xO:Li/n-Si heterojunction solar cells

“…Transparent conducting oxide (TCO)/n-Si [also known as semiconductor-insulator-semiconductor (SIS)] heterojunction SCs (HJSCs) show great promise as low-cost SCs with a high conversion efficiency because of their unique advantages including a simple device structure and a low processing temperature (\250°C) [4][5][6][7][8][9]. Currently, two HJ structures, namely, n-type indium tin oxide (n-ITO)/n-Si and n-type ZnO-base/n-Si, are commonly investigated; the optimal conversion efficiency of which is 16.5 %, as achieved by Kobayashi et al [10], and 9.4 %, as demonstrated in our previous study (Al-Y co-doped ZnO/n-Si) [11], respectively.…”