Bias-dependent spectral tuning in InP nanowire-based photodetectors

Nonpolar-Oriented Wurtzite InP Nanowires with Electron Mobility Approaching the Theoretical Limit

As an important semiconductor nanomaterial, InP nanowires (NWs) grown with a typical vapor-liquid-solid mechanism are still restricted from their low electron mobility for practical applications. Here, nonpolar-oriented defect-free wurtzite InP NWs with electron mobility of as high as 2000 cm² V^-1 s^-1 can be successfully synthesized via Pd-catalyzed vapor-solid-solid growth. Specifically, PdIn catalyst particles are involved and found to expose their PdIn{210} planes at the InP nucleation frontier due to their minimal lattice mismatch with nonpolar InP{2̅110} and {1̅100} planes. This appropriate lattice registration would then minimize the overall free energy and enable the highly crystalline InP NW growth epitaxially along the nonpolar directions. Because of the minimized crystal defects, the record-high electron mobility of InP NWs ( i.e., 2000 cm² V^-1 s^-1 at an electron concentration of 10¹⁷ cm^-3) results, being close to the theoretical limit of their bulk counterparts. Furthermore, once the top-gated device geometry is employed, the device subthreshold slopes can be impressively reduced down to 91 mV dec^-1 at room temperature. In addition, these NWs exhibit a high photoresponsivity of 10⁴ A W^-1 with fast rise and decay times of 0.89 and 0.82 s, respectively, in photodetection. All these results evidently demonstrate the promise of nonpolar-oriented InP NWs for next-generation electronics and optoelectronics.

Room-temperature InP/InAsP Quantum Discs-in-Nanowire Infrared Photodetectors

The possibility to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on a combined study of design, fabrication, and optoelectronic properties of infrared photodetectors comprising four million n⁺-i-n⁺ InP nanowires periodically ordered in arrays. The nanowires were grown by metal-organic vapor phase epitaxy on InP substrates, with either a single or 20 InAsP quantum discs embedded in the i-segment. By Zn compensation of the residual n-dopants in the i-segment, the room-temperature dark current is strongly suppressed to a level of pA/NW at 1 V bias. The low dark current is manifested in the spectrally resolved photocurrent measurements, which reveal strong photocurrent contributions from the InAsP quantum discs at room temperature with a threshold wavelength of about 2.0 μm and a bias-tunable responsivity reaching 7 A/W@1.38 μm at 2 V bias. Two different processing schemes were implemented to study the effects of radial self-gating in the nanowires induced by the nanowire/SiO_x/ITO wrap-gate geometry. Summarized, our results show that properly designed axial InP/InAsP nanowire heterostructures are promising candidates for broadband photodetectors.