University of Texas at El Paso El Paso United States
Through this AFOSR grant, significant progress has been made in setting up chemical vapor deposition capabilities for the synthesis of crystalline two dimensional layered materials as well as developing a residue-free viscoelastic stamping process for nanodevice fabrication involving black phosphorus, NbSe2 and other van der Waals solids. These capabilities were nonexistent in Prof. Kauls group prior to the start of this AFOSR grant. Over the course of the AFOSR grant, the clean viscoelastic stamping process has resulted in suspended membranes of MoS2, black phosphorus and NbSe2 to study their light-matter interactions. As an example, mesoscopic multilayer MoS2 in a metal-semiconductor-metal MSM architecture showed an excellent photoresponse where the dominant photocurrent mechanism was determined to arise from the photoconductive effect PCE, and the external quantum efficiency EQE with gating was determined to be approx. 104. An analysis of the temperature-dependent optoelectronic properties of multilayer black phosphorus BP contacted with Mo electrodes unveiled that the Schottky barrier phiSB of the Mo-BP interface was low, approx. 44.8 meV, which helped in achieving a high photoresponsivity of approx. 4.25 x 104 AW. The thermally driven photocurrent generation mechanism arising from the photobolometric effect PBE dominated the carrier dynamics, particularly for temperatures 175 K, while below this temperature, the photovoltaic effect PVE appeared to be at play. The comparative study on MoS2 devices yielded the broad dominance of the PVE over the entire thermal range 6 K up to 350 K. Finally, the activation energy Ea and the maximum bolometric coefficient betamax were empirically calculated to be approx. 23.5 meV and - 3.85 mSK, respectively. It is notable that this is the highest beta reported on multilayer BP at 350 K.