Characterization of Ag Schottky Barriers on Be_0.02Mg_0.26ZnO/ZnO Heterostructures

Abstract

The BeMgZnO/ZnO heterostructures are capable of producing sufficiently high sheet electron densities to allow field effect transistor operation near or at the LO phonon plasmon resonance frequency for minimal LO phonon lifetimes and high electron velocity. Schottky barriers are imperative for the implementation of the aforementioned devices. Therefore, we have undertaken fabrication and characterization of Ag Schottky barriers on Zn-polar Be 0.02 Mg 0.26 ZnO/ZnO heterostructures, exhibiting the said two-dimensional electron gas (2DEG), grown by molecular beam epitaxy. Ag Schottky barriers are characterized by current-voltage (I-V) measurements in the temperature range from 80 to 400 K. At room temperature, the highest barrier height of 1.07 eV and an ideality factor of 1.22 are achieved with a rectification ratio of about eight orders of magnitude. Richardson constants of 38 AE 22 and 29 AE 20 A cm À2 K À2 are found using modified Richardson plots from Schottky diodes fabricated on two different structures. These values are consistent with the theoretical estimate of 36 A cm À2 K À2 for Be 0.02 Mg 0.26 ZnO. The temperature variation of barrier heights and ideality factors, an aberration from pure thermionic behavior, has been explained with plausible spatial inhomogeneity of barrier height with three Gaussian distributions in the temperature ranges of 80-200, 220-280, and 300-400 K.ZnO as a wide bandgap semiconductor [1] (%3.3 eV at room temperature) with high electron saturation velocity [2] (theoretical 3.5 Â 10 7 cm s À1 ), has garnered popularity owing to its potential for applications in thin film transparent transistors, transparent electrodes for solar cells, light emitters, chemical and biological sensors etc. [1,[3][4][5] Alloying with other II-VI oxides with higher bandgap (MgO and BeO) paves the way for heterojunction field effect transistors with polarization induced two-dimensional electron gas (2DEG). [6,7] Performance of such devices at high electric field, where electron transport is highly controlled by longitudinal optical (LO) phonons, [8] suffers due to accumulation of non-equilibrium hot LO phonons owing to strong electron-LO phonon coupling. Devices operating at or near plasmon-LO phonon resonance exhibit high electron drift velocity [9][10][11] allowed by ensuing ultrafast decay of hot LO phonons, [12,13] which leads to faster electron energy relaxation [14] and optimum device operation conditions (higher frequencies, lower degradation). [8] Plasmon-LO phonon resonance occurs when the energy of the LO phonon becomes similar to the plasmon energy, which occurs in ZnO at a bulk carrier concentration of %7 Â 10 18 cm À3 (ZnO LO phonon energy 72 meV). [14] Clearly, this is far beyond the MESFET operating window (typically 1 Â 10 17 À5 Â 10 17 cm À3 ). The necessity of high electron density makes the use of ZnO heterostructures with 2DEG imperative.Sheet carrier densities up to 8 Â 10 12 cm À2 (corresponding bulk concentration of 2 Â 10 19 cm À3 ) have been reported with MgZnO/ZnO heterostructu...

Analysis of the Current Transport Characteristics (CTCs) in the Au/n-Si Schottky Diodes (SDs) with Al2O3 Interfacial Layer over Wide Temperature Range

“…This case may be described by the lateral inhomogeneity of BHs. [23][24][25][26][27][28][29][30] According to GD model, the formed of BH between semiconductor and Schottky contact hasn't homogenous and a mean-BH ECS Journal of Solid State Science and Technology, 2023 12 083010 ( B0 Φ ¯) is defined in Eq. 9a, depending on the standard-deviation S (σ ) of BH.…”

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

“…Prior to our work 14 , there has been no reports on the investigation of Schottky diodes on BeMgZnO/ZnO heterostructures. Only several studies have reported on Schottky contacts to MgZnO 15 16 , e.g ., with an ideality factor of 2.37, a barrier height of 0.73 eV, and a rectification ratio of only 10 3 15 .…”