Synthesis, electrical transport mechanisms and photovoltaic characteristics of p-ZnIn₂Se₄/n-CdTe thin film heterojunction

Abstract

The synthesis and electrical transport features of vacuum-deposited p-ZnIn₂Se₄/n-CdTe (p-ZIS/n-CT) heterojunction diode (HJD) are discussed. Transmission electron microscopy (TEM) was used to characterize the microstructures of p-ZIS and n-CT thin films. The Hall measurement system determined the conductivity and carrier concentration of the ZIS and CT films; the acceptor concentration (N_a) for ZIS film and donor concentration ($N_{\rm d}$) for CT film observed are $4.12\times {10}^{13}\,\text{cm}^{-3}$ and $2.80\times {10}^{14}\,\text{cm}^{-3}$, respectively. The DC electrical resistance ($R$) variation with temperature (T) determines thermal activation (impurity-based conduction) and bandgap energies of p-ZIS and ${n}\text{-CT}$ thin films. Scanning electron microscopy (SEM) was used to look at the surface morphology of $p\text{-ZIS}/n{\text{-CT HJD}}$. The semiconductor characterization system (SCS-4200) was used to characterize the current–voltage ($I{-}V$) and capacitance–voltage (C–V) of the $p\text{-ZIS}/n\text{-CT HJD}$ at different $T$ ($303{-}340\,\text{K}$). The $p\text{-ZIS}/n\text{-CT HJD}$’s dark $I{-}V$ finding shows conventional diode nature with a decent rectification ratio (RR) ($\simeq\, 4.34\times {10}^{5}\;\text{at}\;\pm 2.0\,\text{V}$). At a given bias, the RR value drops as $T$ increases. The systematic assessment of $I{-}V$ data suggests the thermionic emission (TE) mechanism at lower bias and the space charge-limited conduction (SCLC) mechanism at higher bias. The quantitative analysis estimates the barrier height (${\varphi }_{\rm b}$) as $\simeq\, 0.79\,\text{eV}$ (from $I{-}V$ measurements) and $\simeq\, 0.88\,\text{eV}$ (from C–V measurements). Cheung’s function was utilized to derive the ${\varphi}_{\rm b}$, ideality factor ($n$) and the series resistance ($R_{\rm s}$) of the p-ZIS/n-CT HJD. With a rise in $T$, HJD’s saturation current ($I_{\rm s}$), $n$ and ${\varphi }_{\rm b}$ rise, whilst, $R_{\rm s}$ falls. To gain insight into depletion behaviour, a study examined space charge and electric field distributions for abrupt p-ZIS/n-CT HJD. The experimental findings of Anderson’s model corroborate a theoretical energy band diagram for the p-ZIS/n-CT HJD. The p-ZIS/n-CT HJD’s photovoltaic (PV) characterization resulted in a 0.51 fill factor and 1.04% efficiency. The implications are discussed.