Impact of the base doping concentration on the transport mechanisms in n-type a-SiGe:H/p-type c-Silicon Heterojunctions

Abstract

The charge transport mechanisms occurring in n-type a-SiGe:H on p-type c-Si heterojunctions were determined by analyzing the temperature dependence of the current-voltage characteristics in structures with four different peak base doping concentrations ($N_{B}$ = 1$\times $10$^{15}$, 7$\times $10$^{16}$, 7$\times $10$^{17}$ and 5$\times $10$^{18}$ cm$^{ - 3})$. From the experimental results, we observed that at low forward bias (V$ < 0.45 $V) the current is determined by electron diffusion from the n-type amorphous film to the p-type c-Si for the heterojunction with $N_{B}$ = 1$\times $10$^{15 }$cm$^{ - 3}$, whereas the Multi-Tunneling Capture Emission (MTCE) was identified as the main transport mechanism for the other base doping concentrations. On the other hand, at high forward bias (V$ > 0.45 $V), the space charge limited current effect became the dominant transport mechanism for all the measured devices. Under reverse bias the transport mechanisms depends on the peak base doping, going from carrier generation inside the space charge region for the lowest doping, to hopping and thermionic field emission as the base doping concentration is increased.