Intrinsic carrier multiplication in layered Bi2O2Se avalanche photodiodes with gain bandwidth product exceeding 1 GHz

Abstract

Emerging layered semiconductors present multiple advantages for optoelectronic technologies including high carrier mobilities, strong light-matter interactions, and tunable optical absorption and emission. Here, metal-semiconductor-metal avalanche photodiodes (APDs) are fabricated from Bi 2 O 2 Se crystals, which consist of electrostatically bound [Bi 2 O 2 ] 2+ and [Se] 2− layers. The resulting APDs possess an intrinsic carrier multiplication factor up to 400 at 7 K with a responsivity gain exceeding 3,000 A/W and bandwidth of ~ 400 kHz at a visible wavelength of 515.6 nm, ultimately resulting in a gain bandwidth product exceeding 1 GHz. Due to exceptionally low dark currents, Bi 2 O 2 Se APDs also yield high detectivities up to 4.6 × 10 14 Jones. A systematic analysis of the photocurrent temperature and bias dependence reveals that the carrier multiplication process in Bi 2 O 2 Se APDs is consistent with a reverse biased Schottky diode model with a barrier height of ~ 44 meV, in contrast to the charge trapping extrinsic gain mechanism that dominates most layered semiconductor phototransistors. In this manner, layered Bi 2 O 2 Se APDs provide a unique platform that can be exploited in a diverse range of high-performance photodetector applications.

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

“…The primary parameter is the multiplication factor M , which is directly acquired from the current–voltage ( I – V ) measurements. M is known to follow an empirical formula, 1 – 1/M = ( V / V b ) n where n is the ionization index, for conventional semiconductors, such as Si and Ge, and also 2D materials, such as InSe, black phosphorus, and Bi 2 O 2 Se . Our experiments show that multiplication factors induced from either electrons or holes in ambipolar 2D materials can be measured independently, and the measured relationship between 1 – 1/ M and V ds plotted for both electrons and holes of WSe 2 is provided in Figure a and b, respectively.…”

“…M is known to follow an empirical formula, 1 − 1/M = (V/V b ) n where n is the ionization index, for conventional semiconductors, such as Si 19 and Ge, 18 and also 2D materials, such as InSe, 6 black phosphorus, 11 and Bi 2 O 2 Se. 35 Our experiments show that multiplication factors induced from either electrons or holes in ambipolar 2D materials can be measured independently, and the measured relationship between 1 − 1/M and V ds plotted for both electrons and holes of WSe 2 is provided in Figure 5a and b, respectively. Measurements at various gate voltages show no notable difference between the values of M and the slope of the graphs, which is anticipated because V g influences only the total number of charge carriers involved in the carrier multiplication process but not the lateral field strength that drives the impact ionization in the 2D channel.…”

A New Approach to Designing High-Sensitivity Low-Dimensional Photodetectors

“…In such detectors, light modulates a space charge region (SCR) that acts as a barrier to the transport of majority carriers. The SCR is induced by charge transfer at a heterointerface, such as a type-II semiconductor junction , or Schottky junction, or at any surface with occupied defect states . Upon absorption of a photon, an electron–hole pair is generated and the minority carrier migrates to SCR, modifying the concentration of fixed charge in the trap states.…”

Engineering sensitivity and spectral range of photodetection in van der Waals materials and hybrids

“…This work provides a simple design process and an excellent strategy for highgain room temperature photodetection. Avalanche photodiodes were fabricated by Sangwan et al using layered Bi 2 O 2 Se semiconductor[180]. It works on the principle of carrier multiplication by impact ionization under reverse bias conditions in the depletion region formed at the metal/semiconductor Schottky junction.…”