Investigation On Preparation And Properties Of N Doped And Ag Mono-doped P-type ZnO Films

ZnO, a wide direct band-gap (3.37eV,300K) Ⅱ-Ⅵ compound semiconductor witha large excitation binding energy of60MeV, roughly twice that of semiconductormaterial GaN, and high optical gain (320cm^-1) at room temperture. Therefore, ZnO isone of the most promising candidates for optoelectronic devices such as light-emittingdiodes (LEDs), laser diodes (LDs) and UV photodetectors.To realize practical application of optoelectronic devices based on ZnO materials,it is most essential to grow n and p type ZnO materials with high quality and stability.As is known to all, the p type doping of ZnO presents asymmetry (namely "singlepolarity"), the high quality of n-type conductivity is relatively well understood andcommonly realized through the substitution of a group III element (Al, Ga, In) on a zincsite. However, realization of p-type doping has proven to be much more challenging.Specific challenges include compensation (because of the large background electronconcentration mainly generate by the intrinsic donor defects such as VOand Zni),limited solubility, and deep acceptor levels. To date, the greatest challenge forapplication of optoelectronic devices remains the fabrication of reliable and stablep-type ZnO thin films.At present, how to realize stable and repeatable p type ZnO is very important,simultaneously, the researchers are also trying best to find out the root of instability of ptype ZnO. This subject that is an international problem is eager to solve. Therefore, thispaper mainly focus on finding out the factors which hinder the realization of p type ZnOand lead the instabiliy of p type ZnO.The first part of this paper, the Raman, optical and electrical properties (especiallythe stability of p-type) of ZnO:N film were investigated by Raman scattering spectrum,transmittance spectra and Hall measurement system. The results indicate that all filmsperform the ZnO wurtzite structure. The modes at272.5,505.1and643.6cm^-1can beobserved in the Raman spectra of the ZnO:N film, which can be used as an indicator ofN incorporation into the ZnO film. Hall measurements show that ZnO:N film canbecome p-type after appropriate annealing in nitrogen atmosphere with a holeconcentration of7.73×1017cm^-3, a Hall mobility of3.46cm²V^-1s^-1, and a resistivity of2.34cm. However, it was noted that hole conductivity is not stable based on the Hallmeasurements for a long time. Combined the Raman scattering spectra with firstprinciple calculation, it was concluded that the origin of the instability in ZnO:N results from the compressive stress caused by lattice misfit, as well as the compensation of theN-N pair at the oxygen site (N₂)O.The second part of this paper, the influence of Ag doping content on the electricaland Raman scattering properties of ZnO films were systematically investigated by Hallmeasurement system and Raman scattering spectrum. Two additional local vibrationalmodes (LVMs) at230.0and394.5cm^-1induced by Ag dopant in ZnO:Ag films wereobserved by Raman analyses at RT, corresponding to Ag atoms located at O sites(LVM_Zn-Ag) and Zn sites (LVM_Ag-O) in ZnO lattice. Moreover, we further studied theeffect of donor AgOand acceptor Ag_Zn defects on the electrical properties of ZnO:Agfilms. The results indicate that O-rich condition is preferred to suppress the formation ofAgOdefects and enhance AgZndefects. The p-type ZnO:Ag film was achieved byproperly optimizing the annealing conditions under O-rich condition.