Classical and quantum conductivity in ß-Ga2O3.

The conductivity σ, quantum-based magnetoconductivity Δσ = σ(B) - σ(0), and Hall coefficient RH (= µH/σ) of degenerate, homoepitaxial, (010) Si-doped ß-Ga2O3, have been measured over a temperature range T = 9-320 K and magnetic field range B = 0-10 kG. With ten atoms in the unit cell, the normal-mode phonon structure of ß-Ga2O3 is very complex, with optical-phonon energies ranging from kTpo ~ 20-100 meV. For heavily doped samples, the phonon spectrum is further modified by doping disorder. We explore the possibility of developing a single function Tpo(T) that can be incorporated into both quantum and classical scattering theory such that Δσ vs B, Δσ vs T, and µH vs T are all well fitted. Surprisingly, a relatively simple function, Tpo(T) = 1.6 × 103{1 - exp[-(T + 1)/170]} K, works well for ß-Ga2O3 without any additional fitting parameters. In contrast, Δσ vs T in degenerate ScN, which has only one optical phonon branch, is well fitted with a constant Tpo = 550 K. These results indicate that quantum conductivity enables an understanding of classical conductivity in disordered, multi-phonon semiconductors.

Magnetotransport properties of high quality Co:ZnO and Mn:ZnO single crystal pulsed laser deposition films: pitfalls associated with magnetotransport on high resistivity materials.

The electrical resistivity values for a series of pure and doped (Co, Mn, Al) ZnO epitaxial films grown by pulsed laser deposition were measured with equipment designed for determining the direct current resistivity of high resistance samples. Room-temperature resistances ranging from 7 x 10(1) to 4 x 10(8) Omega/sq were measured on vacuum-reduced cobalt-doped ZnO, (Al,Co) co-doped ZnO, pure cobalt-doped ZnO, Mn-doped ZnO, and undoped ZnO. Using a four-point collinear geometry with gold spring-loaded contacts, resistivities were measured from 295 to 5 K for resistances of < approximately 10(12) Omega/sq. In addition, magnetoresistance and Hall effect were measured as a function of temperature for select samples. Throughout the investigation, samples were also measured on commercially available instrumentation with good agreement. The challenges of transport measurements on high resistivity samples are discussed, along with some offered solutions to those challenges.