Lowering Of Conduction Band Research Articles

Mechanical stress in a tapered channel hole of 3D NAND flash memory

Mechanical stress impact according to the taper angle in 3D vertical NAND flash memory (V-NAND) was investigated using technology computer-aided design simulation (TCAD). In the non-tapered V-NAND, the stress of the polysilicon channel is similar regardless of the number of layers and the position of the WL. On the other hand, in tapered V-NAND, as the taper angle decreases, the CD variation of the channel hole increases, and the compressive stress increases close to the lower WL. The compressive stress applied to the polysilicon channel produces a negative threshold voltage shift (ΔVth) due to conduction band lowering. In tapered V-NAND, the lower WL has a larger ΔVth than the upper WL, and a non-uniform Vth shift occurs. However, as the gate length of the tapered V-NAND is scaled down, the stress of the polysilicon channel is decreased, and the stress difference between the lower WL and upper WL is reduced; therefore, the non-uniform Vth shift is suppressed.

Redshift and amplitude increase in the dielectric function of corundum-like α-(TixGa1−x)2O3

Redshift of the absorption onset and amplitude increase in the ultraviolet complex dielectric function (DF) of corundum-like α-(TixGa1−x)2O3 with increasing Ti content is presented. α-Ga2O3 thin film samples alloyed with Ti up to x=0.61 are grown from plasma enhanced atomic layer deposition. They are characterized by ultraviolet spectroscopic ellipsometry, transmission electron microscopy, and x-ray photoelectron spectroscopy (XPS). The samples are shown to be crystalline up to x=0.053. Ellipsometry is employed to obtain the ordinary complex DF, where the absorption onset shows a strong red shift with increasing Ti content as well as an increase in amplitude, which is associated with a successive take over of Ti related 3d-states in the density-of-states. Valence band XPS results lead to the conclusion that the strong red shift in the absorption onset with increasing Ti content is mainly due to conduction band lowering and less from the valence band.

Impact of Residual Stress on a Polysilicon Channel in Scaled 3D NAND Flash Memory

The effects of residual stress on a tungsten gate in a polysilicon channel in scaled 3D NAND flash memories were investigated using a technology computer-aided design simulation. The NAND strings, with respect to the distance from the tungsten slit, were also analyzed. The scaling of the spacer thickness and hole diameter induced compressive stress on the polysilicon channel. Moreover, the residual stress of polysilicon channel in the string near the tungsten slit had greater compressive stress than the string farther away. The increase in compressive stress in the polysilicon channel degraded the Bit-Line current (Ion) due to stress-induced electron mobility deterioration. Moreover, a threshold voltage shift (∆Vth) occurred in the negative direction due to conduction band lowering.

Photoelectrochemical Response of DSSCs Under Prolonged Reverse Bias and Conduction Band Lowering in Ru‐Complex‐Sensitized TiO2

AbstractTiO2‐based dye‐sensitized solar cells (DSSCs) sensitized with the Ru‐dyes N719 and Z907, are subjected to prolonged reverse bias (RB) by imposing a constant current density of 25 mA cm−2 for up to 1000 h. The temporal changes of the DSSCs during the aging process are followed by the periodical recording of current–voltage curves, electrochemical impedance spectra, charge extraction measurements, and photovoltage decays at the various stages of cell aging. Beside the expected decrease in the concentration of ${{\rm{I}}_3^ - }$ during RB aging, the measurements show a surprising shift of the conduction band edge toward lower energies and a concomitant slowing down of the recombination process with the electrolyte for both DSSCs. This leads to a noticeable improvement in the energy conversion efficiency under low illumination conditions. These unexpected results are discussed on the basis of recent literature reports and attributed tentatively to the adsorption of H+ ions, which are produced during the RB aging, onto the TiO2 surface.

Low turn-on voltage due to conduction band lowering effect in crystalline indium gallium zinc oxide transistors

We found out that in an indium gallium zinc oxide (IGZO) transistor, the energy barrier in the channel region, i.e., the conduction band energy relative to the Fermi energy is lowered by electrons flowing from n+ regions under source and drain electrodes. We have named this phenomenon “conduction band lowering (CBL) effect”. Owing to this effect, even when the Fermi energy of an IGZO film gets closer to the mid-gap, a transistor formed using the film in the channel region is always turned on around a gate voltage of 0 V. In other words, by sufficiently reducing the donor concentration of the channel region, such IGZO transistors are turned on at a certain low gate voltage determined by the CBL effect and their characteristics variation can be suppressed.

Conduction Band Lowering Effect in Crystalline Indium-Gallium-Zinc-Oxide Thin Film Transistors

We have found out that in an IGZO-TFT, the energy barrier, i.e., the conduction band energy relative to the Fermi energy is lowered by electrons flowing from n+ regions under source/drain electrodes to a channel region. We have named this phenomenon “conduction band lowering (CBL) effect”. Owing to this effect, even when the Fermi energy of an IGZO film gets closer to the midgap, a TFT formed using the film is always turned on around V g = 0 V. In other words, by use of an active layer including an IGZO film with a Fermi energy close to the midgap, the CBL effect makes the threshold voltage of I d-V g characteristics converge into a certain low value and the characteristics variation can be suppressed.

Effects of p- and d-block metal co-substitution on the electronic structure and physicochemical properties of InMO 4 (M = Nb and Ta) semiconductors

We have investigated the effect of the co-substitution of Sn IV and Ni II ions on the electronic structure and physicochemical property of InMO 4 (M = Nb, Ta) semiconductors. The co-substitution leads to a red-shift of absorption edge as well as to an appearance of satellite peak below the absorption edge. Depending on the nature of valence orbitals, the substitution of p- and d-block elements results in the lowering of conduction band and the formation of impurity states in the middle of bandgap, respectively. Such a band modification makes the photocatalytic activity of InMO 4 improved against the photodegradation of organic molecules.

Strained Pt Schottky diodes on n-type Si and Ge

The variation of electron barrier height and built-in voltage of Pt Schottky diodes on the mechanically strained n-type Si and Ge is investigated experimentally and theoretically. The mechanical strain is measured by Raman spectroscopy and analyzed by the finite element method. The built-in voltage and barrier height measured by capacitance-voltage and current-voltage methods, respectively, decrease with increasing external tensile strain. The reduction of the built-in voltage and barrier height originates mainly from the conduction band lowering with strain. The extracted value of conduction band lowering is consistent with the theoretical calculations using the “stress-free” boundary condition.

Double-transconductance-plateau characteristics in InGaAs/GaAs real-space transfer high-electron-mobility transistor

Bias-tunable double-transconductance-plateau characteristics due to real-space transfer through the lowering of conduction band offset at high electric fields in a δ-doped InGaAs/GaAs high-electron-mobility transistor have been observed. Extrinsic, unpassivated peak performance values, with gate dimensions of 1×125 μm2, include the transconductance plateaus of 269 and 116 mS/mm at VDS=3 V for VGS=0 V and −1.5 V, respectively, maximum drain current density of 382 mA/mm at VDS=5.5 V, unity current gain cutoff frequency of 15.5 GHz, and maximum frequency of oscillation of 23 GHz. The present structure is promising for high-speed analog-to-digital converters or multiple-state quantizer applications.