Channel-Length-Modulated Avalanche Multiplication in Ambipolar WSe₂ Field-Effect Transistors

Abstract

Recently there has been growing interest in avalanche multiplication in two-dimensional (2D) materials and device applications such as avalanche photodetectors and transistors. Previous studies have mainly utilized unipolar semiconductors as the active material and focused on developing high-performance devices. However, fundamental analysis of the multiplication process, particularly in ambipolar materials, is required to establish high-performance electronic devices and emerging architectures. Although ambipolar 2D materials have the advantage of facile carrier-type tuning through electrostatic gating, simultaneously allowing both carrier types in a single channel poses an inherent difficulty in analyzing their individual contributions to avalanche multiplication. In ambipolar field-effect transistors (FETs), two phenomena of ambipolar transport and avalanche multiplication can occur, and both exhibit secondary rise of output current at high lateral voltage. We distinguished these two competing phenomena using the method of channel length modulation and successfully analyzed the properties of electron- and hole-initiated multiplication in ambipolar WSe2 FETs. Our study provides a simple and robust method to examine carrier multiplication in ambipolar materials and will foster the development of high-performance atomically thin electronic devices utilizing avalanche multiplication.

Efficient Avalanche Photodiodes with a WSe2/MoS2 Heterostructure via Two-Photon Absorption

“…By using the linear fitting of the plot (the red line), we obtained n = 11.3. It should be noted that the obtained n value for the WSe 2 /MoS 2 heterostructure device is higher than the one for the monolayer WSe 2 device …”

“…The multiplication factor (M) can be obtained by the equation M = I dark /I s . 28 I s is the saturation current and can be defined as I dark at V = V cr . 38 Figure 2d shows ln(1 − 1/M) versus ln(V).…”

“…In contrast, when the reverse bias is above V cr , the strong electric field induces the avalanche multiplication process, leading to the multiplication of the holes. It should be noted that MoS 2 and WSe 2 serve as the multiplication channels for electrons and holes, respectively. , …”

“…The critical voltage ( V cr ) is determined to be 6.5 V (the blue line) where the dark current begins to increase superlinearly (the red dashed line represents the linear fitting line of the dark current before the avalanche effect occurs). The multiplication factor ( M ) can be obtained by the equation M = I dark / I s …”

“…By applying a moderate bias of >6.5 V, we observe a clear avalanche multiplication of electrons and holes, which respectively occur in WSe 2 and MoS 2 monolayers. 28,29 For the TPA-based photodetection, the avalanche effect with an ultrahigh gain of ∼1300 improves the responsivity by nearly 3 orders of magnitude, resulting in the record-high responsivity of 88 μA/W among TPA-based infrared photodetectors reported thus far. This work presents a new possibility of 2D materials for building practical infrared photodetectors for photonic-integrated circuits.…”