Fig. 1. (a) Crystal structure of the 2D b-As_0.5P_0.5 layers. First row: top view and right view; Second row: side view. (b) Raman spectra of the 2D b-As_0.5P_0.5 layers. (c) XRD pattern of the 2D b-As_0.5P_0.5 layers. (d) Atomic force microscopic image of the PDs. White dashed line: metal electrode; red dashed line: b-As_0.5P_0.5 material. (e) Height profile obtained along with the white line in (d). (f) Tauc plot of the b-As_0.5P_0.5 PDs. The inset shows the FTIR spectra of the PDs.

Fig. 2. (a) Schematic diagram of the hBN-encapsulated b-As_0.5P_0.5 PDs under IR illumination. (b) The 2D mapping plot of the current under 638 nm laser illumination as a function of the V_ds and the incident laser power. (c) The 3D mapping plot of the photocurrent at V_ds = 1 V under 1550 nm laser illumination. (d) Energy band diagram of the b-As_0.5P_0.5 and the electrode metal (before and after contact). E_f, Fermi level; CB, conduction band; VB, valence band. (e) Energy band diagram of the b-As_0.5P_0.5 PD at a bias voltage V_ds under illumination. I_pc, photoconductive current.

Fig. 3. (a) Temporal photoresponse of the PDs at different wavelengths with fixed incident power at V_ds = 1 V. (b) Wavelength dependence of the R_i and EQE_i at V_ds = 1 V. (c) Wavelength dependence of the NEP_i and D_i^* at V_ds = 1 V. (d) Rising and falling times for the PDs under a 1550 nm laser illumination at V_ds = 1 V. (e) Comparison of the wavelength detection range and the responsivity of our device with other IR PDs (b-P^{[3335" target="_self" style="display: inline;">–35]}, b-As_0.83P_0.17^[36], Gr^[37], Gr/GaAs^[38], MoTe₂^[39], MoTe₂/Si^[40], MoS₂/BP^[41], MoS₂/CdTe^[42], PtSe₂^[43], PtS₂/PtSe₂^[44], and Tellurene^[45]). (f) Comparison of τ_rise and τ_fall of our device with other IR PDs under a 1550 nm laser illumination (b-P^[46], b-As_0.83P_0.17^[36], Bi₂O₂Se/BP^[47], BP/WSe₂^[48], Gr/Ge^[49], Gr/InGaAs^[50], Gr/1T^′-MoTe₂/Si^[51], MoS₂/BP^[52], PbSe-CQDs^[53], PdTe₂/Si^[54], WSe₂/SnSe₂^[55], and ZnSb^[56]).

Fig. 4. (a) Schematic diagram of an IR optical communication application. (b) Transmitted ASCII code of “AsP” under a 1550 nm laser illumination. I_dark = 50 µA.

Fig. 5. (a) Experimental setup for single-pixel-based IR imaging with the b-As_0.5P_0.5 PDs under a 1550 nm laser illumination. (b) Optical imaging mask for “ACSII.” (c)–(e) Optical imaging results at different bias voltages (V_ds = 0.01, 0.1, and 1 V).