Determination of the Band Alignment of a‐IGZO/a‐IGMO Heterojunction for High‐Electron Mobility Transistor Application

Abstract

In the past decade, amorphous InGaZnO thin film transistors (a-IGZO TFTs) have become a very promising candidate for application in flat panel displays (FPDs). However, it is difficult to break through the mobility bottleneck of a-IGZO TFTs to obtain mobilities higher than 100 cm 2 V À1 s À1 , thus limiting their use in more advanced applications. Construction of a high-electron mobility transistor (HEMT) based on a heterojunction structure could provide a solution for this problem. In this work, the band alignment of a-IGZO and amorphous InGaMgO (a-IGMO) heterojunction has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission spectra measurements. The valence band (DE V ) and conduction band offsets (DE C ) were determined as 0.09 and 0.83 eV, respectively. The DE C was large enough to construct a potential well that could favor the appearance of a twodimensional electron gas (2DEG). Hence, the achievement of an HEMT based on a-IGZO/a-IGMO heterojunction can be expected. Moreover, band bending contributed greatly to such a large DE C , and thus to the formation of electrical confinement structure. Our findings suggest that a-IGZO/a-IGMO heterojunction is a potential candidate for constructing a HEMT and thus breaking through the mobility bottleneck of a-IGZO-based TFTs for the applications in next-generation electronic products.In the past decade, a-IGZO thin film transistors (TFTs) have proven to be one of the most promising candidates for the applications in flat panel displays (FPDs) as a result of their excellent uniformity, high transparency to visible light, and large field effect mobility (m FE , over 10 cm 2 V À1 s À1 ). [1,2] Researchers have been attempting to increase the mobility m FE of a-IGZO TFTs in order to realize displays with higher resolution, faster frame rate, and larger panel size. For instance, Wu et al. [3] obtained an a-IGZO TFT with a m FE of 33.5 cm 2 V À1 s À1 by using an atmospheric-pressure-plasma-treated SiO 2 gate dielectric. The a-IGZO TFT with HfLaO gate dielectric was treated in a CHF 3 /O 2 plasma, thus increasing the m FE to an ultrahigh value of 39.8 cm 2 V À1 s À1 . [4] Recently, Zheng et al. [5] reported a highmobility a-IGZO TFT (m FE > 60 cm 2 V À1 s À1 ) with an atomic-layer-deposited SiO 2 gate insulator. Nevertheless, the m FE of a-IGZO TFTs is still not high enough, especially for satisfying some more advanced applications such as 3D displays, flexible logic circuits, and system-on-panel devices. [1] According to previous studies, an extremely high carrier mobility can be realized in the HEMT based on a heterojunction structure due to the space separation of the two-dimensional electron gas (2DEG) and ionized donors. For instance, the AlGaN/GaN heterojunction that was widely adopted to form HEMTs can yield a 2DEG, thus increasing the electron mobility to over 1500 cm 2 V À1 s À1 . [6] A ZnMgO/ZnO heterojunction reveals the potential for a high-frequency and high-power HEMT application due to the large 2DEG-induced mobility of 250 cm 2

Tailoring the Band Alignment of Gax Zn1-x O/InGaZnO Heterojunction for Modulation-Doped Transistor Applications

“…Besides, the spectra were fitted using the Lorentzian–Gaussian method with a Shirley background subtraction. The C 1s peak was referenced to the binding energy of 284.8 eV to offset the binding‐energy shift induced by surface charging . In addition, the thicknesses of the deposited films were measured by the Veeco Dektak 150 surface profiler.…”

Tunable Band Alignment of Phase-Engineered Two-Dimensional MoS2 Monolayers

“…In general, there are type Ι (straddling gap) and type ΙΙ alignments (staggered gap), where the type ΙΙ staggered alignment has been used for photodetector owing to the effective charge distribution that is ascribed to the separation of photogenerated carriers toward opposite direction across the interface. , In the case of the type I alignment, it has the advantage of the multiple quantum well structure enabling the development of high-performance light-emitting diodes exhibiting the high emission efficiency . Based on the XPS analysis results demonstrating the shifts of binding energies in the phase-engineered MoS 2 /SiO 2 heterojunctions, the band bending was revealed at the interface of phase-engineered MoS 2 /SiO 2 heterojunctions owing to the interfacial dipoles, where various factors have shown to contribute to the interfacial dipole such as interfacial defects and interfacial layer, and charge transfer across the interface. , The huge changes in the band alignments at various phase-engineered MoS 2 /SiO 2 heterojunctions were clearly observed, ascribed to the expansion of E g MoS 2 and increased VBM of the MoS 2 monolayer as the phase transition from 1T’- to 2H-phase occurred. This can vary depending on the degree of phase engineering, such as the portion of the 1T’- and 2H-phase content in the hybrid 1T’/2H-phase MoS 2 , where the expansion of E g MoS 2 can increase with increasing the portion of the 2H-phase, as well as changes in the optical and electrical properties such as Raman, UV–vis, and XPS spectra exhibiting more 2H-phase-like features as shown elsewhere. , Considering that the phase-engineered TMDs exhibiting superior electrical, chemical, and catalytic properties can be great promise for a broad range of applications including field-effect transistors, photovoltaics, biomedical devices, and electrocatalytic hydrogen evolution, ,− this modulation of energy band structures and the change in the band alignments at the interfaces with phase-engineered TMDs can provide the evidence for the operation mechanism of various TMD-based electronic devices with the charge transfer phenomena at the interfaces.…”

“…33 Based on the XPS analysis results demonstrating the shifts of binding energies in the phaseengineered MoS 2 /SiO 2 heterojunctions, the band bending was revealed at the interface of phase-engineered MoS 2 /SiO 2 heterojunctions owing to the interfacial dipoles, where various factors have shown to contribute to the interfacial dipole such as interfacial defects and interfacial layer, and charge transfer across the interface. 19,34 The huge changes in the band alignments at various phase-engineered MoS 2 /SiO 2 heterojunctions were clearly observed, ascribed to the expansion of E g MoS 2 and increased VBM of the MoS 2 monolayer as the phase transition from 1T'-to 2H-phase occurred. This can vary depending on the degree of phase engineering, such as the portion of the 1T'-and 2H-phase content in the hybrid 1T'/2H-phase MoS 2 , where the expansion of E g MoS 2 can increase with increasing the portion of the 2H-phase, as well as changes in the optical and electrical properties such as Raman, UV−vis, and XPS spectra exhibiting more 2H-phase-like features as shown elsewhere.…”

Analysis of Interface Phenomena for High-Performance Dual-Stacked Oxide Thin-Film Transistors via Equivalent Circuit Modeling

“…To address this issue, dual-stacked OS-based TFTs have been considered as potential candidates to improve field-effect mobility. − However, they still have insufficient field-effect mobility (30–60 cm 2 /V·s), considerably low on–off current ratio (<10 6 ), undesirable threshold voltage far from 0 V, or unstable reliability caused by bias stress. When the threshold voltage is formed far from 0 V and the on–off ratio is low, power consumption occurs even at the off-state, which can cause reliability problems such as degradation of display devices.…”