Effect of Ga substitution for In in LiInSe₂ crystals on carrier transport behaviors and alpha particles detection

Due to high density of ⁶Li isotope and the ability to respond to ionizing radiation through direct charge carrier transport, Li-containing chalcogenides are expected to be the replacement of ³He-tube or neutron reactive material coated semiconductor films for thermal neutron detection. However, the neutron detection efficiency of ⁶LiInSe₂ is limited to 82% ascribed to that ¹¹⁵In isotope captures neutrons and generates gamma rays, which deteriorated the neutron response. Neutron detection efficiency could be improved by gallium substitution since its low neutron capture cross-section. In this work, the electron and hole mobility (μ) of LiIn_1−xGa_xSe₂(x = 0, 0.25, 0.5, 0.75, 1) were studied by first-principles density functional theory (DFT) calculation, which demonstrated the electron mobility (μ_e) of LiIn_0.5Ga_0.5Se₂ is close to that of LiInSe₂ while the hole mobility (μ_h) is much improved. To further certify, both LiIn_0.5Ga_0.5Se₂ and LiInSe₂ crystals were grown under similar condition by vertical Bridgman method, exhibited comparable bandgap and bulk resistivity at room temperature. The charge transport behaviors were evaluated under ²⁴¹Am@5.48MeV alpha particles. The full energy peak is clearly resolved in the pulse height spectra. The electron and hole mobility-lifetime products of LiIn_0.5Ga_0.5Se₂ are 1.5×10⁻⁵ cm²/V and 6.9×10^{− 5} cm²/V, respectively. The resulting μ_e of LiIn_0.5Ga_0.5Se₂ and LiInSe₂ crystals are 270 cm²V⁻¹s⁻¹ and 180 cm²V⁻¹s⁻¹, respectively, fitted by time of flight (TOF) technique. In addition, the μ_h of LiIn_0.5Ga_0.5Se₂ is obtained with the value of 110 cm²V⁻¹s⁻¹, but the hole response is too weak to be resolved for LiInSe₂.