Effect of electron irradiation on InAs〈Sn〉 microcrystals grown by chemical transport method

Abstract

The results of experimental studies of the effect of electron irradiation (13 MeV, 300 К) on the electrophysical properties of n-InAs whiskers are reported. The limiting electrophysical parameters and the Fermi-level pinning in the irradiated material are discussed.InAs occupies a special place among the III-V semiconductor compounds due to the peculiarities in changes of the electrophysical properties under high-energy electron, proton, and neutron irradiation. In irradiated InAs, the Fermi level is pinned in the region of the allowed energy levels of conduction band in the proximity of E v + 0.5 eV at 77-300 К in contrast to the majority of III-V compounds, where the Fermi level is always shifted to the band gap under irradiation by electrons, protons, and fast neutrons [1][2][3]. Over many years, this special feature of InAs was thought to be due to the preferred formation of hydrogen-like radiation-induced donor defects in the lattice of this semiconductor [4,5]. However, the investigations of heavily doped n + -InAs (n + ≈ 2·10 19 cm -3 ) showed that the acceptor defects are also formed in this material exposed to high-energy irradiation [3]. It was concluded that both donor and acceptor radiation-induced defects are formed in InAs under irradiation as in other III-V semiconductors. The efficiency of the influence of these defects on the electrophysical properties depends only on the doping level and conductivity type of the initial material. Conceivably, the efficiency of formation of various radiation-induced defects also depends on the Fermi level position, as it does, for example, in GaAs [6]. It should be noted that up to date, the radiation-induced defects in InAs irradiated by electrons were mainly studied in the bulk material [3,7].In this work, we for the first time present the results of investigations into 10×0.1×0.05 mm InAs microcrystals (whiskers) grown by a chemical transport method. This material is characterized by a higher structural perfection and lower density of growth dislocation as compared with bulk InAs, which results in higher charge-carrier mobility. The initial InAs crystals were doped by the amphoteric impurity Sn up to the free-electron concentrations (6.5·10 16 -1.5·10 18 ) cm -3 . The electrophysical parameters of the InAs samples were measured at 300 K using a precision test bench TI-3 made in the laboratory of magnetic sensors of the National University "Lvov Polytechnics" on the basis of an HMS 7504 facility (Lake Shore, USA). The measurement error of the relative change in the charge-carrier concentration was ±0.01%. The samples were irradiated by 13 MeV electrons up to the fluences F = 1.0·10 16 , 8.0·10 16 , and 1.6·10 17 сm -2 using a pulse accelerator "Mikrotron M 30" at the department of nuclear processes of the Institute of Electron Physics of the National Academy of Sciences of the Ukraine (Uzhgorod). The following beam parameters were used: beam current 50 µA, pulse duration 0.2-0.3 ms, and pulse frequency 2 kHz. The irradiation temperature (273-300 К) was maintain...