Incompatibility of standard III–V compound semiconductor processing techniques with terbium-doped InGaAs of high terbium concentration

Abstract

Terbium-doped InGaAs with a high terbium concentration shows promise as a high-efficiency thermoelectric material, with the thermal conductivity dropping to 1.27 W/m K at a TbAs concentration of 1.55% by number of atoms. However, large discrepancies are noted in Hall effect measurements on terbium-doped InGaAs grown by molecular beam epitaxy on InP substrate following standard III–V wet chemical processing techniques, when compared to samples with no processing beyond deposition of indium contacts. These discrepancies preclude systematic exposition of temperature- and composition-dependent thermoelectric figures of merit. The discrepancy is seen to be correlated with the terbium concentration and the thickness of the active material. The steps in the process sequence are examined under controlled conditions. Although the exact cause for the discrepancy has not been found, some of the obvious reasons have been ruled out. It is therefore surmised that (1) chemical reaction with photoresist, (2) ultraviolet irradiation during photolithography, or (3) reaction with photoresist developing solutions and HF are the factors responsible for the changes in Hall voltage. Evidence is presented for the creation of surface states that corrupt Hall effect measurements on the bulk semiconductor.