This study presents a comprehensive investigation of the composition ( \(Cd\) mole fraction m, \( 0 \, < \, m \, < \, 1\) ) and temperature-dependent (20–400 K) optoelectronic and electrophysical properties of \(p{\text{Si}}/n{\text{Cd}}_{m} {\text{Z}}_{1 - m} {\text{S}}\) heterojunctions. A hybrid approach combining analytical modeling, numerical simulations, and experimental validation was employed to capture the effects of incomplete dopant ionization, dielectric bowing, and temperature on key device parameters. Standard doping concentrations of \(p \, = \, 1 \times 10^{16} {\text{cm}}^{ - 3}\) \(p - {\text{Si}}\) and \(n \, = \, 4 \times 10^{16} {\text{cm}}^{ - 3}\) \(n{\text{Cd}}_{m} {\text{Z}}_{1 - m} {\text{S}}\) were used. The study quantifies temperature- and composition-dependent bandgap energy \(Eg\left( {T,m} \right)\) , Debye temperature \(\Theta \left( m \right)\) , built-in electric field \(E\left( {T,m,x} \right)\) , and junction capacitance. As \({\text{Cd}}\) content increases, the bandgap of \(n{\text{Cd}}_{m} {\text{Z}}_{1 - m} {\text{S}}\) decreases from ~3.6 eV ( \({\text{ZnS}}\) -rich) to ~2.42 eV ( \({\text{CdS}}\) -rich), while Si maintains a thermally stable bandgap (~ 1.1–1.17 eV), resulting in a favorable type-II band alignment ( \(\Delta Eg \, > \, 1.25\,eV\) ). The decrease in \(\Theta \left( m \right)\) enhances phonon scattering and modifies recombination behavior. The derived analytical expression for \(E\left( {T,x} \right)\) explicitly incorporates incomplete ionization, enabling prediction of space charge and electric field distribution at cryogenic temperatures. The model shows excellent agreement with experimental data, emphasizing the critical role of temperature and composition in charge transport. These results highlight the potential of \(p{\text{Si}}/n{\text{Cd}}_{m} {\text{Z}}_{1 - m} {\text{S}}\) heterostructures for high-performance optoelectronic devices operating under variable thermal and vibrational conditions.
