Interband quantum tunneling of electrons in semiconductors is of intense recent interest as the underlying transport mechanism in tunneling field-effect transistors. Such transistors can potentially perform electronic switching with lower energy than their conventional counterparts. The recent emergence of 2-dimensional semiconducting crystals provides a new material platform for realizing such devices. In this work, we derive an analytical expression for understanding tunneling current flow in 2D crystal semiconductors. We apply the results to a range of 2D crystal semiconductors, and compare it with tunneling currents in 3D semiconductors. We also discuss the implications for tunneling devices.
Theoretical investigation of direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and quantum well interband tunnel junctions for multi-junction solar cells
Electronic transport in narrow gap semiconductors is characterized by spontaneous vertical transitions between carriers in the valence and conduction bands, a phenomenon also known as Zener tunneling. However, this effect is not captured by existing models based on the Boltzmann transport equation. In this work, we propose a new fully first principles model for electronic transport using the Wigner distribution function and implement it to solve the equations of motion for electrons. The formalism generalizes the Boltzmann equation to materials with strong interband coupling and include transp…
Ultra-violet emitters have several applications in the areas of sensing, water purification, and data storage. While the III-Nitride semiconductor system has the band gap region necessary for ultraviolet emission, achieving efficient ultraviolet solid state emitters remains a challenge due to the low p-type conductivity and high contact resistance in wide band gap AlGaN-based ultra-violet light emitters. In this work, we show that efficient interband tunneling can be used for non-equilibrium injection of holes into ultraviolet emitters. Polarization-engineered tunnel junctions were used to enh…
By the insertion of thin InGaN layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the…
We study spin-dependent transport properties in magnetic tunneling junctions (MTJs) with semiconductor barriers, Fe/CuInSe$_2$/Fe(001) and Fe/CuGaSe$_2$/Fe(001). By analyzing their transmittances at zero bias voltage on the basis of the first-principles calculations, we find that spin-dependent coherent tunneling transport of $Δ_1$ wave functions yields a relatively high magnetoresistance (MR) ratio in both the MTJs. We carry out a detailed analysis of the band-resolved transmittances in both the MTJs and find an absence of the selective transmission of $Δ_1$ wave functions in some energy regi…
Magnetic layered van der Waals crystals are an emerging class of materials giving access to new physical phenomena, as illustrated by the recent observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest in semiconductors is the interplay between magnetism and transport, which has remained unexplored. Here we report first magneto-transport measurements on exfoliated CrI3 crystals. We find that tunneling conduction in the direction perpendicular to the crystalline planes exhibits a magnetoresistance as large as 10 000 %. The evolution of the magnetoresistance with magnetic f…
In 2D-semiconductor-based field-effect transistors and optoelectronic devices, metal-semiconductor junctions are one of the crucial factors determining device performance. The Fermi-level (FL) pinning effect, which commonly caused by interfacial gap states, severely limits the tunability of junction characteristics, including barrier height and contact resistance. A tunneling contact scheme has been suggested to address the FL pinning issue in metal-2D-semiconductor junctions, whereas the experimental realization is still elusive. Here, we show that an oxidized-monolayer-enabled tunneling barr…
Tunneling atomic force microscopy (TUNA) was used at ambient conditions to measure the current-voltage ($I$-$V$) characteristics at clean surfaces of highly oriented graphite samples with Bernal and rhombohedral stacking orders. The characteristic curves measured on Bernal-stacked graphite surfaces can be understood with an ordinary self-consistent semiconductor modeling and quantum mechanical tunneling current derivations. We show that the absence of a voltage region without measurable current in the $I$-$V$ spectra is not a proof of the lack of an energy band gap. It can be induced by a surf…
In this paper, we have built a numerical p-n Si/GaAs heterojunction model using a quantum-mechanical tunneling theory with various quantum tunneling interfacial materials including two-dimensional semiconductors such as hexagonal boron nitride (h-BN) and graphene and ALD-enabled oxide materials such as HfO2, Al2O3, and SiO2. Their tunneling efficiencies and tunneling current with different thicknesses were systematically calculated and compared. Multiphysics modeling was used with the aforementioned tunneling interfacial materials to analyze changes in strain under different temperature condit…
Group-IV-based ferromagnetic semiconductor Ge1-xFex (GeFe) is one of the most promising materials for efficient spin injectors and detectors for Si and Ge. Recent first principles calculations (Sakamoto et al., Ref. 9) suggested that the Fermi level is located in two overlapping largely spin-polarized bands formed in the bandgap of GeFe; spin-down d(e) band and spin-up p-d(t2) band. Thus, it is important to clarify how these bands contribute to spin injection and detection. In this study, we show the first successful observation of the tunneling magnetoresistance (TMR) in magnetic tunnel junct…
Scanning Tunneling Microscopy of Defect States in the Semiconductor Bi$_2$Se$_3$
Bi $_2$ Se $_3$掺杂过量Bi的扫描隧道光谱图像揭示了具有类似三叶草叶子的引人注目的形状的电子缺陷状态。用一个简单的紧束缚模型，我们表明，在Bi $_2$ Se $_3$的缺陷态的几何形状可以直接相关的位置的起源杂质。只有Bi缺陷的Se网站五个原子层以下的表面实验观察到。我们发现，这种效果可以解释的缺陷和表面电子结构的相互作用。
Research in two-dimensional (2D) materials has experienced rapid growth in the past few years. In particular, various layered compounds exhibiting quantum phenomena, such as superconductivity and magnetism, have been isolated in atomically thin form, often in spite of their chemical instability. The nature of the 2D phases can be different than their bulk counterparts, making such systems attractive for fundamental studies. Owing to their high crystallinity and absence of dangling bonds, devices and heterostructures incorporating these materials may also show performance exceeding that of trad…
Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials
实现了反向击穿电压在-3 V ~-15 V范围内可精确调节而对正向电流-电压曲线无任何影响的有机齐纳二极管。这是通过以1纳米的精度控制pin二极管中的电荷耗尽区的宽度来实现的，而与掺杂浓度和本征层的厚度无关。击穿效应具有指数的电流-电压特性和弱的温度依赖性，这是由穿过邻近分子HOMO-LUMO能隙的隧穿机制解释的。实验数据证实了一个最小的哈密顿模型的方法，包括相干隧穿和非相干跳跃过程作为可能的电荷传输路径通过有效的器件区域。
We theoretically analyse band-to-band tunneling (BTBT) in highly-mismatched, narrow-gap dilute nitride and bismide alloys, and quantify the impact of the N- or Bi-induced perturbation of the band structure -- due to band-anticrossing (BAC) with localised impurity states -- on the electric field-dependent BTBT generation rate. For this class of semiconductors the assumptions underpinning the widely-employed Kane model of direct BTBT break down, due to the strong band edge nonparabolicity resulting from BAC interactions. Via numerical calculations based on the Wentzel-Kramers-Brillouin approxima…
A vertical spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) is a promising low-power device for the post scaling era. Here, using a ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs channel layer, we demonstrate a large drain-source current IDS modulation by a gate-source voltage VGS with a modulation ratio up to 130%, which is the largest value that has ever been reported for vertical spin field-effect transistors thus far. We find that the electric field effect on indirect tunneling via defect states in the GaAs channel layer is responsible for the…
