High-performance Diodes Based On CuI/Si Heterojunction And Its Photoelectric Response

In recent years,the p-type semiconductor copper iodide(CuI)has attracted great attention in the field of photodetection due to its wide bandgap,good light transmittance,and good electrical conductivity.Because the luminescence of CuI is mainly concentrated in the band edge,and the intensity of defect luminescence is low,it has the potential of excellent optoelectronic material.At present,the wavelength detection range of photovoltaic devices based on CuI heterojunctions is mostly concentrated in the ultraviolet band.Moreover,limited by the high carrier concentration in the body,the heterojunction generally exists in the form of an n-p⁺junction,which leads to a very low minority carrier diffusion length on the CuI side,so the photovoltaic based on CuI heterojunction It is also difficult to make breakthroughs in the quantum efficiency of these devices.In this paper,Si and CuI are selected to form a high-performance heterojunction diode device,which has a large rectification ratio and extends the photoelectric response of this heterojunction to the visible light range.On the other hand,by doping with bromine,the intrinsic carrier concentration of CuI is reduced by more than an order of magnitude,and a p-n⁺heterojunction based on CuI is prepared.It provides a new method for the subsequent preparation of high-performance ultraviolet photodetectors.The main contents and innovations of this paper are as follows:(1)An n-p⁺-type CuI/Si heterojunction diode was prepared by the solid-phase iodization method,and its rectification ratio was 7.6×10~4,which was much higher than that of CuI diodes prepared by other chemical methods.This work introduces the main preparation process of CuI/Si heterojunction diodes and compares the two groups of diode devices before and after the formation of ohmic contact.The rectification ratio of the diode without good ohmic contact is 1×10~3,and the rectification ratio after improving the contact can reach 7.6×10~4.In addition,the results of the I-V test were fitted by the Shockley equation,the ideality factor of the diode was obtained as 2.11,and its physical cause was explained.(2)The carrier concentration of CuI was reduced by bromine doping,and p-n⁺-type CuI/Si heterojunction diodes were prepared,which proved that the electrical transport properties of CuI are well tolerant to defects such as lattice distortion.In this work,the influence of bromine impurity introduction on CuI films was studied,a suitable range of bromine doping was determined by using XRD and SEM,and the electrical properties of CuI films with different bromine contents were studied.Among them,CuI with a bromine content of 19.7%has successfully reduced the carrier concentration from 4.36×10¹⁹ cm^-3 to 2.80×10¹⁸ cm^-3.In addition,the luminescence mechanism of CuI thin films was studied by PL and CL spectra.Finally,the band structures before and after bromine doping are analyzed based on the results of physical characterization.In terms of device fabrication,the performance of the p-n⁺junction is improved by introducing a CuI interlayer,and the tunneling effect between bromine-doped CuI and heavily doped silicon is suppressed.(3)Based on the n-p⁺type CuI/Si heterojunction,a high-performance photodiode with an"ultraviolet-visible"dual-band detection mode is realized under different bias voltages,and its detectivity can reach 10¹³?10¹⁴ Jones,which is a much higher than other Cu-based photodetectors.This work systematically studies the photocurrent generation mechanism of n-p⁺type CuI/Si heterojunction.I-V and I-t tests were carried out under the irradiation of400 nm,505 nm,635 nm,and 780 nm lasers,respectively.The device behaves as a visible light detector at a bias voltage of 0 V,and the photoresponse extends to the ultraviolet band at a bias voltage of-3 V.When operating in the linear region,the EQE produced by the 635 nm laser can reach 175%,and even the 400 nm laser,which produces the smallest EQE,has an EQE value of 48%.In the I-t test,the ratio of photo-dark current of the device is relatively stable,does not fluctuate with the pulsed laser,and the response time is stable at around 0.5 s.