Carrier compensation behaviors in Si-doped AlxGa1-xAs epilayers due to thermal annealing

Abstract

Heavily doping methods into semiconductor epilayers have attracted attention because of the interest in both an increase of the conductance of an active layer and an reduction of the electrical resistance to improve the device performance of electronic and optoelectronic devices [1–3]. Among various heavily doped epilayers, heavy Si doping in Alx Ga1−x As layers is particularly interesting due to the enhancement of the intermixing behavior of group III atoms resulting from the formation of the compensation centers such as Ga vacancies [4–6]. Even though few works concerning the compensation mechanisms in semi-insulating GaAs have been performed [7], investigations of the mechanisms in Si-doped Alx Ga1−x As layers due to thermal annealing have not yet been done. This letter reports on Van der Pauw-Hall effect measurements which were carried out to determine the carrier density and the mobility of as-grown and annealed Si-doped Alx Ga1−x As layers and photoluminescence (PL) measurements which were performed in order to investigate the optical behaviors in the layers. A possible compensation mechanism is presented on the basis of the experimental results. The Alx Ga1−x As epilayers studied in this work were grown on semi-insulating GaAs(100) substrates by using molecular beam epitaxy (MBE). The surface of the substrate was cleaned chemically with acetone, trichloroethylene, methanol and deionized water, alternately. The substrates were etched in a H2SO4 : H2O2 : H2O (5 : 1 : 1) solution for 90 s and rinsed in deionized water thoroughly. After the GaAs wafers were cleaned chemically, they were mounted onto a molybdenum susceptor by soldering using indium. Prior to Alx Ga1−x As growth, the substrates were thermally cleaned in order to remove the oxide layer at 600 ◦C for 10 min in As atmosphere in the growth chamber at a pressure of 2.5 × 10−6 Torr. Alx Ga1−x As epilayers were deposited onto a GaAs buffer layer with 1 μm thickness. After a 100-A undoped Al0.25Ga0.72As layer was grown, a 2000-A Si-doped Al0.25Ga0.75As active layer was grown. The rapid thermal annealing (RTA) process was performed in a nitrogen atmosphere with a tungsten-halogen lamp as the thermal source, and