氢气引入对宽光谱Mg和Ga共掺杂ZnO透明导电薄膜的特性影响

Influence of H_2 introduction on wide-spectrum Mg and Ga co-doped ZnO transparent conductive thin films

为适应宽光谱高效率硅基薄膜太阳电池的应用需求,本文尝试采用直流磁控溅射技术在553 K衬底温度下生长氢化Mg和Ga共掺杂ZnO(HMGZO)透明导电氧化物(TCO)薄膜.通过对薄膜微观结构、表面形貌、电学以及光学性能的测试和分析,详细地研究了氢气(H2)流量(0—16.0 sccm)对HMGZO薄膜结晶特性及光电性能的影响.实验结果表明:生长获得的HMGZO薄膜均为六角纤锌矿结构的多晶薄膜,择优取向为(002)晶面生长方向.薄膜的生长速率随着氢气流量的增加呈现逐渐减小趋势,主要归因于溅射产额的减小.适当的氢气引入会引起晶粒尺寸的增加.随着氢气流量由0增加至4.0 sccm,ZnO薄膜电阻率从177?·cm急剧减小至7.2×10-3?·cm,主要是由于H施主的引入显著地增加了载流子浓度;然而进一步增加氢气流量(4.0—16.0 sccm)造成电阻率的轻微增加,主要归因于载流子浓度的减小以及过多氢杂质引入造成杂质散射的增加.所有生长获得的HMGZO薄膜平均光学透过率在波长λ～320—1100 nm范围内可达87%以上.由于Mg的作用及Burstein-Moss效应的影响造成了带隙展宽,带隙变化范围～3.49—3.70 eV,其中最大光学带隙Eg可达～3.70 eV.

To meet the demands of high efficient silicon thin film solar cells, transparent conductive hydrogenated Mg and Ga co-doped ZnO （HMGZO） thin films were deposited via pulsed direct current （DC） magnetron sputtering on glass substrates at a substrate temperature of 553 K. The micro-structural, morphological, electrical, and optical properties of HMGZO thin films were investigated at various H2 flow rates. Experimental results show that all the HMGZO thin films are polyerystalline with a hexagonal wurtzite structure exhibiting a preferred （002） crystal plane orientation. Appropriate H2 flow rate increases grain size and also enhances the RMS roughness. The deposition rate of HMGZO films decreases with the increase of H2 flow rate due to the decrease of sputtering yield. Resistivity of HMGZO thin films decreases rapidly from 117 to 7.2 × 10-3 Ωcm with increasing H2 flow rate from 0 to 4.0 sccm. With further increasing H2 flow rate （4.0-16.0 sccm）, the resistivity increases slightly due to the reduced carrier concentration and excessive H atoms as impurity. Optical transmittance of all the HMGZO thin films is higher than 87.7% in the wavelength range from 320 to 1100 nm. Burstein-Moss band-filling determined by carrier concentrations and the incorporation of Mg atoms together contribute to the band-gap （Eg） widening phenomenon. The band gap Eg varies from ～ 3.49 -3.70 eV and the maximum Eg of 3.70 eV is obtained at a H2 flow rate of 16.0 sccm.