MoTe₂PN Homojunction Constructed on a Silicon Photonic Crystal Cavity for High-Performance Photodetector

We demonstrate a straightforward construction of MoTe2 PN homojunction on a silicon photonic crystal cavity, which promises the realizations of cavity-enhanced optoelectronic devices integrated on silicon photonic chips. The employed silicon photonic crystal cavity has an air-slot in the middle to split it into two parts, which directly function as two individual back-gate electrodes of the top-coated few-layer MoTe2. Beneficial from MoTe2's ambipolar property, reconfigured (PN, NN, PP, NP) homojunctions are realized by controlling the gate voltages of the two separated silicon electrodes. For instance, on/off ratios exceeding 104 are obtained from the PN or NP homojunctions, and the ideality factors could approach 1.00. On the other hand, the silicon photonic crystal cavity could enhance light absorption in the coated MoTe2, promising high-performance photodetection. By coupling the resonant mode with the MoTe2 PN junction, a high photoresponsivity of 156 mA/W is obtained at the wavelength of 1353.7 nm, though it is the limit of MoTe2's absorption bandedge. As attributes of the PN junction, the photodetector has a dark current as low as 0.14 nA and a response bandwidth exceeding 1.1 GHz. The proposed device geometry has advantages of employing silicon photonic crystal cavity as the back gates of MoTe2 PN junction directly and simultaneously to enhance light-MoTe2 interactions, which might open a new avenue to construct MoTe2-based laser diodes and electro-optic modulators on silicon photonic chips.