Yutaka Koga

Photoconductivity and Photo-Hall Effect of p-Type InSe Single Crystals

Measurements of photoconductivity and photo-Hall effect have been made on Zn-doped p-type InSe in the temperature range from 220 to 330 K. The results are interpreted by a two-carrier model under illumination assuming that Δn=Δp, where Δn and Δp are the photogenerated carrier concentration of electrons and holes, respectively. The obtained mobility ratio b is determined as 9.5×10-2T0.7, and the temperature dependence of the hole mobility can be well fitted by the model developed by Schmid (Nuovo Cimento B21 (1974) 258).

Fundamental Absorption Edge of γ-InSe

Optical absorption edge spectrum of γ-InSe single crystals has been investigated. The experimental results show that the fundamental absorption edge is well interpreted by the transition to the two-dimensional indirect exciton state, where only a single phonon participates.

Carrier Transport Mechanisms of InSe p-n Homojunction

InSe p-n homojunctions have been fabricated by bringing the cleavage surfaces (c-plane) of undoped n-type and Zn-doped p-InSe into direct contact. The mechanisms of carrier transport across the junction in the dark and under illumination are investigated by current-voltage, capacitance-voltage characteristics and spectral response of the short-circuit current. The experimental results indicate that this homojunction fabrication method is effective for electrical and optoelectronic devices.

Optical and electrical properties of C+-implanted GaAs

Abstract Carbon (C) was implanted into extremely pure GaAs grown by molecular beam epitaxy in a wide range of C dose [C] from 1 × 10 16 to 1 × 10 20 cm −3 . The impurity levels and the process of crystalline recovery were investigated by using Raman scattering, photoluminescence and the Hall effect. The implanted layers were found to form a crystalline layer at an annealing temperature around 200°C for [C] smaller than 1 × 10 17 cm −3 , while for [C] over that value this temperature became extremely high with increasing [C] and it reached around 550° for [C] =1 × 10 20 cm −3 . The well-defined below-band gap emission, [g-g], exclusively inherent to acceptor impurities was a dominant one for [C] lower than 3 × 10 17 cm −3 but its intensity was suppressed for [C] higher than this value. From the results of Hall effect, the current peculiar features of [g-g] were found to be attributable to the low substitutional efficiency of C atoms as acceptors.

Annealing Behavior of Zn-Doped p-Type InSe

Photoluminescence measurements were carried out to study the annealing effect of Zn-doped p-type InSe. The diffusion constant of Zn atom along the c-axis in InSe was estimated to be D=2.7×107 exp (-2.5 eV/kT)cm2s-1 from the depth profiles of the 1.17 eV emission peak intensity. The isochronal annealing behavior of this peak showed that the activation energy for a dissociation of Se vacancy-Zn acceptor complex was 0.4 eV.