p-type doping for transparent perovskite semiconductor of alkali-earth stannate and its pn-junctions

Abstract

Abstract Transparent oxide semiconductors (TOSs) are widely used as transparent electrodes because they are optically transparent in the visible light and UV regions and their electrical conductivity can be manipulated. However, applications of TOSs are limited to transparent electrodes and panel displays because of a lack of p-type conducting transparent oxide materials. The discovering and developing Cu-based p-type TOSs has allowed the fabrication of fundamental semiconductor devices such as pn junctions and field effect transistors

however, there are few reports of TOS materials that can be injected with dopants to from both p- and n-type materials. Recently, it was reported that La-doped BaSnO3 (BLSO) has high oxygen stability and good electrical conductivity. However, even though BSO thin films exhibit a high epitaxiality, the films contains many grain boundaries and dislocations that act as charge traps and scattering centers. We are attempting to find a substrate more suitable than SrTiO3 (STO) for improving the electrical properties of BLSO thin films

however, BLSO thin films on alternative substrates show a poorer mobility than those on STO. In addition, the low doped BLSO thin film acts like a p-type semiconductor due to the effects of threading dislocations even though the dopant is an n-type carrier. Because the d-orbital does not participate in the bonding between Sn and O in BaSnO3 (BSO), this bond can be stronger than that in other perovskite materials, and allows for the possible doping with a p-type carrier. We have been successfully in doping BSO with K using pulsed laser deposition. Although K-doped BSO exhibits a rather high resistivity at room temperature, its conductivity increased dramatically at higher temperatures. The activation energy of the K-dopant was estimated to be about 0.5 eV. Furthermore, the conductivity decreased when a small amount of oxygen was removed from the film, consistent with the behavior of p-type doped oxides. The results of doping BSO with other elements such as Ga and Cu are presented. We have fabricated pn junctions using K-doped BSO (BKSO) and BLSO as the p- and n-type semiconductors, respectively. I-V characteristics of these devices showed the typical rectifying behavior of pn junctions in room temperature. In addition, I-V characteristics of these devices exhibit an ideal diode behavior with the ideality factor between 1 and 2 in high temperature, implying high integrity of the BSO materials. Moreover, the junction properties were found to be very stable after repeated high-bias, high-temperature thermal cycling. Our demonstration of pn junctions based on a single perovskite BSO further enhances the potential of a transparent perovskite semiconductor BSO system, whose high mobility and stability have previously been shown. We investigated SrSnO3 (SSO), which has a 4 eV direct band gap. SSO thin films were deposited on KTaO3 (KTO) to minimize the lattice mismatch with SSO. Images obtained with TEM and AFM showed that the SSO thin films on KTO exhibit almost no threading dislocations. In measuring the electrical properties of the SSO thin films with various dopants such as Sb, La and Ru, we found that the mobility was generally lower than that of BLSO thin films due to tilting of the SnO6 octahedral. Ru-doped SSO showed p-type behavior even at room temperature. We fabricated a pn junction using Sb-doped SSO and Ru-doped as the n- and p-type semiconductors, respectively. We found that the current of the SSO based pn junction was higher than that based on BSO system

there were several problems with the pn junction, such as large leakage current and large parasitic resistance. If we combine the BSO and SSO system, however, it will be possible to fabricate LED devices because of the direct band gap, low leakage current pn junction and low resistivity conduction.