Structural, band and electrical characterization of β-(Al0.19Ga0.81)2O3 films grown by molecular beam epitaxy on Sn doped β-Ga2O3 substrate

Abstract

We characterized unintentionally doped β-(Al0.19Ga0.81)2O3 for its structural, band, and electrical properties by using a variety of material and electrical characterization methods such as atom probe tomography (APT), transmission electron microscope, X-ray photoelectron spectroscopy (XPS), capacitance-voltage measurement, and a temperature dependent forward current-voltage measurement. A 115 nm thick β-(Al0.19Ga0.81)2O3 film was grown by molecular beam epitaxy on Sn doped Ga2O3 substrates. Reciprocal space mapping shows a lattice matched (Al0.19Ga0.81)2O3 layer. Both APT and TEM results confirm a sharp β-(Al0.19Ga0.81)2O3/β-Ga2O3 interface. XPS measurements show conduction band offsets of 2.78 ± 0.25 eV and 0.79 ± 0.25 eV between the SiO2/β-(Al0.19Ga0.81)2O3 and β-(Al0.19Ga0.81)2O3/β-Ga2O3 interfaces, respectively. Extracted room temperature Schottky Barrier Heights (SBHs) after zero field correction for Pt, Ni, and Ti were 2.98 ± 0.25 eV, 2.81 ± 0.25 eV, and 1.81 ± 0.25 eV, respectively. The variation of SBHs with metals clearly indicates the dependence on work function.

Probing structural and chemical evolution in (AlxGa1−x)2O3 using atom probe tomography: A review

“…The bandgap in (Al x Ga 1−x ) 2 O 3 tends to increase monotonically with the incorporation of Al content [12,13] that forms (Al x Ga 1−x ) 2 O 3-/Ga 2 O 3 heterostructures with large band offset [9]. This elevated bandgap has enabled successful realization of (Al x Ga 1 −x ) 2 O 3 based field-effect transistors [11,14,15,16], Schottky barrier diodes [17,18], and photodetectors [19,20,21].…”

“…APT combined with field ion microscopy (FIM) and time-of-flight (TOF) spectroscopy [55] is a powerful characterization technique that enables direct 3D visualization of complex structure and chemistry at the atomic level with very high sensitivity [10 atomic parts per million (appm)] [45,56] as well as near-atomic spatial and chemical resolution [57]. Over the last decade, APT has been widely used to study the atomic-level structural chemistry including local elemental segregation/clustering, layer homogeneity, interface RMS roughness, adatoms diffusions across the interfaces in wide bandgap semiconductors, and their heterostructures to explain local chemical and physical properties that directly manipulate the corresponding electrical/optical devices [18,58,59,60,61,62,63,64,65,66,67,68,69]. In addition to all these capabilities, atom collection in APT experiments provides their position coordinates, TOF, and mass-to-charge states (m/q) of each atom [57].…”

Behavior of the ε-Ga2O3:Sn Evaporation During Laser-Assisted Atom Probe Tomography

“…The ε polymorph is more interesting for technological applications because it has a hexagonal closed packed structure, presenting a remarkable advantage in terms of heteroepitaxial growth on substrates like GaN, AlN, ZnO, or c-plane sapphire (Bosi et al, 2020). Very recently some studies were carried out by using APT to investigate the 3D element distribution in Ga 2 O 3 and (Al x Ga 1− x ) 2 O 3 under different growth conditions (Oshima et al, 2016; Swinnich et al, 2019; Vaidya et al, 2019). However, an in-depth study of experimental conditions and physical processes leading to deviations from the expected Ga/O ratio equal to 2/3 (the Ga 2 O 3 stoichiometric composition) is still missing.…”

Theoretical investigation of optical intersubband transitions and infrared photodetection in β-(AlxGa1 − x)2O3/Ga2O3 quantum well structures

“…A large CBO is achieved in β-Ga2O3 by alloying with Aluminum. β-(AlxGa1-x)2O3 is predicted to be stable at concentrations up to x = 0.7 [34]; at this concentration, the bandgap increases to 6.3 eV with a type-II band-alignment [33,35,36] and nearly no valence band discontinuity-CBOs of up to 1.7 eV are theoretically available [33,34]. In addition, recent density functional theory (DFT) predictions show gamma-valley electrons isolated by at least 2 eV to neighboring valleys [37].…”