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.

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β-Ga2O3, an emerging ultrawide bandgap (UWBG) semiconductor, offers promising properties for next-generation power electronics, chemical sensors, and solar-blind optoelectronics. Scaling down of β-Ga2O3 to the atomic level affords the advantages of two-dimensional (2D) materials, while maintaining the inherent properties of the parent bulk counterpart. Here, we demonstrate a simple approach to synthesize ultrathin millimeter-size β-Ga2O3 sheets using a liquid gallium squeezing technique. The GaOx nanolayer produced by stamping liquid gallium under the Cabrera–Mott oxidation was converted into few-atom-thick β-Ga2O3 via thermal annealing under atmospheric conditions. This approach was also applied to various substrates such as SiO2, Si, graphene, quartz, and sapphire to heteroepitaxially synthesize 2D β-Ga2O3 on a target substrate. Finally, we propose a patterning strategy combining the squeezing technique with conventional lithography to obtain a β-Ga2O3 layer with a controllable thickness and shape. Our synthetic method has the potential to overcome the limitations of conventional β-Ga2O3 growth methods, paving a path for applications in UWBG-based (opto-)electronics with a high throughput in a cost-effective manner.

Cushing syndrome (CS) is a rare disease caused by hypercortisolemia. Although surgical treatment is the first-line treatment in CS, the appropriate medication for the patient’s condition should be selected when medical treatment is needed. Etomidate is an adrenal-blocking drug used to treat CS and the most suitable for severe hypercortisolemia and adrenocortical carcinoma (ACC), due to cardiovascular stability and an anti-tumorigenic effect. However, its use and safe recommended dosage in infants with CS is unreported. Here we describe the case of a 2-month-old girl treated with etomidate for CS caused by ACC. Even though radical mass excision was performed, severe hypercortisolemia persisted, resulting from metastatic lesions in the liver, and medical treatment was considered. The etomidate doses, no bolus dose and infusion rate of 0.03 mg/kg/hour, may be an appropriate dose for severe hypercortisolemia in infants. This case will help determine future treatment strategies for similar cases in infants.

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