Daniel Splith

Schottky contacts to In2O3

n-type binary compound semiconductors such as InN, InAs, or In2O3 are especial because the branch-point energy or charge neutrality level lies within the conduction band. Their tendency to form a surface electron accumulation layer prevents the formation of rectifying Schottky contacts. Utilizing a reactive sputtering process in an oxygen-containing atmosphere, we demonstrate Schottky barrier diodes on indium oxide thin films with rectifying properties being sufficient for space charge layer spectroscopy. Conventional non-reactive sputtering resulted in ohmic contacts. We compare the rectification of Pt, Pd, and Au Schottky contacts on In2O3 and discuss temperature-dependent current-voltage characteristics of Pt/In2O3 in detail. The results substantiate the picture of oxygen vacancies being the source of electrons accumulating at the surface, however, the position of the charge neutrality level and/or the prediction of Schottky barrier heights from it are questioned.

Oxide bipolar electronics: materials, devices and circuits

We present the history of, and the latest progress in, the field of bipolar oxide thin film devices. As such we consider primarily pn-junctions in which at least one of the materials is a metal oxide semiconductor. A wide range of n-type and p-type oxides has been explored for the formation of such bipolar diodes. Since most oxide semiconductors are unipolar, challenges and opportunities exist with regard to the formation of heterojunction diodes and band lineups. Recently, various approaches have led to devices with high rectification, namely p-type ZnCo2O4 and NiO on n-type ZnO and amorphous zinc-tin-oxide. Subsequent bipolar devices and applications such as photodetectors, solar cells, junction field-effect transistors and integrated circuits like inverters and ring oscillators are discussed. The tremendous progress shows that bipolar oxide electronics has evolved from the exploration of various materials and heterostructures to the demonstration of functioning integrated circuits. Therefore a viable, facile and high performance technology is ready for further exploitation and performance optimization.

Method of choice for fabrication of high-quality ZnO-based Schottky diodes

We present a comprehensive comparison of electrical properties of differently fabricated high quality Schottky contacts on ZnO thin films grown by pulsed laser deposition. Thermally evaporated Pd/ZnO Schottky contacts exhibit ideality factors as low as 1.06 due to their high lateral homogeneity. The effective Richardson constant determined using these homogeneous contacts is (7.7±4.8)A cm−2 K−2 close to the theoretical value of 32 A cm−2 K−2. However, their rectification ratio is at most five orders of magnitude due to their comparably small barrier height ( ≈0.7eV). The largest effective barrier height ( 1.11 eV) and rectification ratio ( 7×1010) was obtained for reactively sputtered PdOx/ZnO Schottky contacts. Eclipse pulsed laser deposited IrOx/ZnO Schottky contacts were found to combine very good lateral homogeneity ( n≈1.1), with a reasonably large barrier height ( 0.96 eV) and large rectification ratio ( ≈9 orders of magnitude). Our results for differently fabricated Schottky contacts suggest that t...

Structural and optical properties of (In,Ga)2O3 thin films and characteristics of Schottky contacts thereon

We report on structural and optical properties of a (InxGa)2O3 thin film having a monotonic lateral variation of the indium content x (). The growth condition for each In content is similar allowing precise determination of the dependence of material properties on x. For low In content () the thin film has monoclinic crystal structure; for highest In contents () the cubic bixbyite phase is predominant. For intermediate alloying we observe additionally the rhombohedral InGaO3(II) crystallographic phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (InxGa)2O3 and photo response measurements for

Comparison of Schottky contacts on β-gallium oxide thin films and bulk crystals

The electrical properties of identically fabricated PtOx Schottky contacts on -oriented gallium oxide thin films and bulk crystals were investigated using current–voltage measurements at room temperature. The homogeneous barrier height of the Schottky contacts on thin films is 1.55 ± 0.15 eV, which is significantly smaller than that of those fabricated on bulk single crystals, 2.01 ± 0.12 eV. This large difference indicates an upward band bending of 0.4–0.5 eV at the surface of the bulk crystals in the as-received state, which is explained by the larger net doping density of the thin films compared to the single crystals.

Modeling of Schottky barrier diode characteristics on heteroepitaxial β-gallium oxide thin films

When investigating Schottky contacts on heteroepitaxial β-Ga2O3 thin films, several non-idealities are observed in the current voltage characteristics, which cannot be accounted for with the standard diode current models. In this article, we therefore employed a model for the rigorous calculation of the diode currents in order to understand the origin of this non-idealities. Using the model and a few parameters determined from the measurements, we were able to simulate the characteristics with good agreement to the measured data for temperatures between 30 °C and 150 °C. Fitting of the simulated curves to the measured curves allows a deeper insight into the microscopic origins of said non-idealities.