Study On P-type Doping And Photodetectors Of MgZnOS

Zinc oxide（Zn O）is a direct band-gap semiconductor material with a band gap of 3.37e V and an exciton binding energy of 60 me V.It not only has excellent luminescence properties,but also is affordable,environmentally friendly,non-toxic and easy to obtain.Due to the above characteristics,Zn O has great potential in the field of optoelectronics.However,in order to realize the practical application of Zn O semiconductor materials,the following two problems need to be solved urgently:one is the energy band engineering of Zn O materials;the second is the development of high-quality bipolar（n-type and p-type）Zn O materials.At present,the energy band regulation of Zn O has been realized by means of anion and cation doping.In terms of bipolar doping,Zn O is an intrinsic n-type semiconductor material,and its n-doping is easy to realize;the stable p-type doping of Zn O has not been solved due to the low solid solubility of N acceptor,deep acceptor level and high intrinsic carrier concentration.Literature research shows that a small amount of Mg doping can broaden the optical band gap of Zn O while maintaining the hexagonal wurtzite structure of Zn O,doping of Mg increases its conduction band bottom and inhibits its intrinsic donor（oxygen vacancy）ionization to produce background electrons.On the other hand,an appropriate amount of S element doping can effectively reduce the N acceptor formation energy and acceptor energy level.Therefore,the valence band top and conduction band bottom of Zn O can be improved by co-doping with Mg and S elements,which can effectively reduce the activation energy of N acceptor（produce more holes）and suppress the intrinsic background electrons,so as to realize the efficient and stable p-type doping of Mg Zn OS alloy.In this paper,Mg Zn OS thin films were deposited by pulsed laser deposition（PLD）at different oxygen pressures to realize the band gap control.On the basis of this,the preparation of p-type conductive Mg Zn OS:N thin films was successfully realized by using NO as the reaction gas.On this basis,a new type of p-Mg Zn OS:N/n-Zn O quasi-homogeneous p-n junction type self-driven ultraviolet photodetection model device was constructed.The main research topics and experimental results are as belows:1.A series of Mg Zn OS quaternary alloy films were prepared on c-plane sapphire substrates by changing the growth oxygen pressure with self-made Mg Zn OS ceramics as the target and O₂as the reaction gas.The structure,morphology and optical band gap evolution of the films were studied.Furthermore,parallel Au electrodes were evaporated on the surface of Mg Zn OS thin films to explore the preparation of MSM photodetectors,and the photoelectric properties of the detectors were preliminarily tested.The results show that the prepared Mg_0.20Zn_0.80O_1-xS_xfilm has a wurtzite structure and c-axis orientation,and has a relatively smooth surface.As the growth oxygen pressure increases from 0 Pa to 4 Pa,the S content in Mg_0.20Zn_0.80O_1-xS_xfilms decreases from 66%to 7%,and the optical band gap increases from3.23 e V to 3.71 e V according to E_g=3.78+1.46x+0.96x².The test results of MSM photodetectors show that with the increase of oxygen pressure,the photocurrent ratio of the detector increases first and then decreases,and the relaxation time increases gradually.2.A series of Mg Zn OS:N thin films with different Mg contents were prepared on c-plane sapphire substrates by PLD method using self-made Mg Zn OS ceramics with different Mg contents as target materials and high purity NO as reaction gas.The microstructure,optical and electrical properties of the films were studied,and p-type conductivity was successfully realized in Mg Zn OS films.The results show that the prepared Mg Zn OS:N film（Mg content in the target<0.30）is a high-quality c-axis oriented quasi-epitaxial film.With the increase of Mg content in the film from 5%to 49%,the optical band gap of the film increases from 3.17 e V to 3.75 e V,following the law of E_g=3.05+0.08y+0.002y².The conduction type of Mg_0.09Zn_0.91O_0.75S_0.25:N thin film is p-type when the content of Mg in the target is 4%.The carrier concentration（n）of the film is 2.02×10¹⁹cm^-3,the Hall mobility（μ）is 0.25 cm²/V·s,and the resistivity（ρ）is 1.25Ω·cm.3.On the basis of the above p-type conductive Mg Zn OS:N film,Zn O and n-Mg Zn OS were used as n-type layers,respectively.By evaporating Al and Au electrodes on the n and p layers,a novel n-Zn O/p-Mg Zn OS:N junction and n-Mg Zn OS/p-Mg Zn OS:N junction photoelectric detection model device were explored and prepared,which realized self-driven detection of 350 nm wavelength ultraviolet light.The results show that the n-Zn O/p-Mg Zn OS:N junction and n-Mg Zn OS/p-Mg Zn OS:N junction exhibit obvious rectification characteristics,and the turn-on voltages are 1.21 V and 0.24 V,respectively.The response time of the n-Zn O/p-Mg Zn OS:N detector isτ_rise=0.69 s,τ_decay=0.33 s,the responsivity is2.26 m A/W and the detectivity is 2.67×10¹¹Jones（@350 nm）at 0 V bias.The response time of n-Mg Zn OS/p-Mg Zn OS:N detector at 0 V bias isτ_rise=0.13 s,τ_decay=0.07 s,and the responsivity is 0.086 m A/W（@350 nm）.It can be seen from the performance comparison that the photodetector with Mg Zn OS as the n-type layer can shorten the response time of the device,but it is not conducive to the improvement of the responsivity of the device.