Non-metal to metal transition in n-type ZnO single crystal materials

Abstract

The electrical properties of ZnO mono-crystalline materials, either in the form of bulk crystals or epitaxial films, were investigated for a large range of un-intentional or intentional doping concentrations extending from 4.0×1015 cm−3 up to 1.3×1020 cm−3. Hall and resistivity measurements were carried out from 10 K to 300 K, yielding the temperature dependent carrier densities and carrier mobilities. This allowed for an unambiguous determination of the dopant ionization energies, taking into account the concentration of compensation centers. The ionization energy variation as a function of dopant concentration was found to follow Mott's law, being consistent with the hydrogenic behavior of all involved donors; an effective critical Mott's concentration for the insulator to metal transition was found to be around 4.2×1018 cm−3, while the apparent value of the isolated donor ionization energy was determined as being 60 meV.

Locally‐Strain‐Induced Heavy‐Hole‐Band Splitting Observed in Mobility Spectrum of p‐Type InAs Grown on GaAs

“…These values are different from the literature data of E a ≈ 20 meV . However, it is well known that as the dopant concentration increases, the dopants start to interact and form an impurity band . The increase in the width of this band decreases the ionization energy .…”

“…However it is well known that as the dopant concentration increases, the dopants start to interact and form an impurity band [33][34][35]. The increase of the width of this band decreases the ionization energy [33][34][35][36]. For sufficiently high dopant concentration the associated broad impurity band and the conduction (valence) band edge merge leading to the negative ionization energies.…”

Optical Phase Transition in Semiconductor Quantum Metamaterials

“…To demonstrate this novel approach, we rely on ISB transitions in ð1010Þ ZnO=ðZn; MgÞO MQWs [19]. High quality nonpolar ZnO heterostructures can be grown on bulk ZnO substrates at high doping concentration (well above 10 19 cm −3 ) [20][21][22], which facilitates the control of the ISB transitions by avoiding the quantum confined Stark effect. The structures were grown by molecular beam epitaxy (MBE) on m-plane ZnO substrates.…”

Terahertz Intersubband Electroluminescence from Nonpolar m-Plane ZnO Quantum Cascade Structures

“…Compared with GaAs THz QCLs, the sample shows the stronger temperature-dependence of the injection current, as depicted in the inset of Figure 4a. This can be explained by the large ionization energy of the Ga dopant in the ZnO heterostructure 36 (see Supporting Information, Figure 3). An ionization energy of 6.7 meV, corresponding to a temperature of 78 K, was obtained for sample ZOE1, leading to a strong temperature-dependence of the free carrier density and, thus, the injected current.…”