Recessed-Channel WSe₂ Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching

Abstract

Effective channel control with low contact resistance can be accomplished through selective ion implantation in Si and III–V semiconductor technologies; however, this approach cannot be adopted for ultrathin van der Waals materials. Herein, we demonstrate a self-aligned fabrication process based on self-terminated p-doping and layer-by-layer chemical etching to achieve low contact resistance as well as a high on/off current ratio in ultrathin tungsten diselenide (WSe2) field-effect transistors (FETs). Damage-free layer-by-layer thinning of the WSe2 channel is repeated up to a thickness of approximately 1.4 nm, while maintaining the selectively p-doped source/drain regions. The device characteristics of the recessed-channel WSe2 FET are systematically monitored during this layer-by-layer recess-channel process. The WSe2 etching rate is estimated to be 2–3 layers per cycle of oxidation and subsequent chemical etching. The self-terminated tungsten oxide (WOX) layer grown through ultraviolet–ozone treatment induces robust p-doping in the neighboring (or underlying) WSe2 through the electron withdrawal mechanism, which remains in the source/drain regions after channel oxide removal. The adopted self-terminated and self-aligned recess-channel process for ultrathin WSe2 FETs enables the realization of a high on/off output current ratio (>108) and field-effect mobility (∼190 cm2/V·s), while maintaining low contact resistance (0.9–6.1 kΩ·μm) without a postannealing process. The proposed facile and reproducible doping and atomic-layer-etching method for the fabrication of a recessed-channel FET with an ultrathin body can be helpful for high-performance two-dimensional semiconductor devices and is applicable to post-Si complementary metal-oxide semiconductor devices.

Self‐Powered 2D MoS2/WOx/WSe2 Heterojunction Photodetector Realized by Oxygen Plasma Treatment

“…[ 34 ] WO x has a bandgap of 2.0 eV from 4.5 eV CBM (conduction band minimum) to 6.5 eV VBM (valence band maximum) and is sandwiched between MoS 2 and WSe 2 . [ 35,36 ] Furthermore, we believe that the WO x contributed to the enhancement of I photo / I dark ratio by acting as tunneling barrier to reduce dark current. To confirm this, we fabricated multiple devices with similar thickness of WSe 2 and MoS 2 flakes and measured dark current by sweeping the drain bias as shown in Figure S2 (Supporting Information).…”

Nanostructured doping of WSe2via block copolymer patterns and its self-powered photodetector application

“…As WO x with a high work-function makes the neighboring WSe 2 electron-deficient, the underlying WSe 2 can be p-doped using the charge-transfer process. 23 The oxidation of WSe 2 has been intensively investigated using laser annealing, 54 oxygen plasma, 55 UV-ozone treatment, 56 and thermal annealing 24 under oxygen ambient conditions. Yang et al effectively constructed seamless WSe 2 homojunction diodes by converting the top few layers of WSe 2 to WO x ( x < 3) via 325 nm laser exposure.…”

p-Type Conversion of WS2 and WSe2 by Position-Selective Oxidation Doping and Its Application in Top Gate Transistors

“…Therefore, in addition to WS 2 , WSe 2 is also selected for this study. Recently, a p-type operation has been investigated for relatively thick WSe 2 by back gate (BG) control, through selective formation of a WO x layer on WSe 2 . − However, the effects of WO x formation on the FET performance are still unclear. It has not yet been clarified whether WSe 2 just below the metal electrode is oxidized, and disadvantages associated with WO x formation, such as hysteresis caused by trap sites in WO x , have not been evaluated.…”