Influence of spontaneous polarization on the electrical and optical properties of bulk, single crystal ZnO

Abstract

Hall effect, photoluminescence, and Schottky diode measurements were made on the Zn-polar and O-polar faces of undoped, bulk, single crystal, c-axis ZnO wafers. Significant polarity related differences were observed in the PL and Schottky diode characteristics of low carrier concentration, hydrothermally grown wafers. Increased emission from free exciton recombinations and from recombinations between 3.3725 and 3.3750eV was observed on the Zn-polar face. Conversely, emission between 3.3640 and 3.3680eV was more intense on the O-polar face. The barrier heights of silver oxide Schottky diodes were approximately 130meV larger on the Zn-polar face compared to the O-polar face.

Crystal orientation dependent thermoelectric properties of highly oriented aluminum-doped zinc oxide thin films

“…These bound polarization charges induce a Schottky barrier potential at every Zn-polar surfaces which reduce effective mass and r along the c-axis. 6,16 It has also been found 17 that though both c-polar planes and a-planes in ZnO accumulate electrons, owing to the spontaneous polarization the former accumulates more electrons. Since r and Hall effect in our films were measured in-plane, the relevant effective mass that determines the transport is the in-plane effective mass, i.e., along directions in the c-plane of c-AZO film (film B) and along directions in the a-plane of a-AZO films (films C and E).…”

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

“…3,9,10 Stabilization mechanisms of Zn͑0001͒-or O͑0001͒-terminated faces are still controversial, yet few experimental studies compare them. 11 Differences between hydrothermal ZnO polar surfaces were ascribed to surface band bending induced by spontaneous polarization, 12 while melt-grown ZnO exhibits only a small difference in band bending. 13 It is still not clear which polar face should give better Schottky contacts because few comparisons between two polarities exist regarding their surface optical properties, defect concentrations, metal reactivities with various metal contacts, and Schottky barrier heights.…”

Electrical characteristics of palladium Schottky contacts to hydrogen peroxide treated hydrothermally grown ZnO

“…In addition, it has been suggested [20] that a higher Schottky barrier height (φ B ) is expected on the Zn-face as an effect of an upward band bending on this face caused by the intrinsic polarization. However, the samples studied in this thesis were cut with the c-axis perpendicular to the surface and excellent Pd SCs were obtained on the O-face.…”

“…However, despite the first SC to ZnO was reported by Mead [51] already in 1965, it is still challenging to realize stable and high quality SCs. For instance, the presence of a conductive surface layer due to group III ions [53], native defects both resident in the bulk and created by the metallization [54], processing [55], adsorbates [56,57], sample orientation [58,59] and presence of surface dipoles [60], can all affect the ZnO surface and the metal-semiconductor junction performance. Similar effects can account for the wide scatter, up to ∼ 2 eV in the ZnO work function (i.e.…”