铝镓氮薄膜双光子吸收效应

基于飞秒激发Z扫描实验技术,研究了氮化镓薄膜和不同铝掺杂含量的掺铝氮化镓(以下简称铝镓氮)薄膜的超快非线性光学响应特性。在开孔Z-scan测试中,纯Ga N晶体薄膜表现出典型的双光子吸收特性,双光子吸收系数为3.5 cm/GW,且随着激发光强的增大而逐渐减小。随后测试了不同铝掺杂含量的Al_xGa_(1-x)N薄膜的非线性吸收系数。结果表明,随着铝掺杂摩尔分数的提高(0,19%,32%,42%),非线性吸收系数逐渐减小(18,10,6,5.6 cm/GW)。结合半导体非线性吸收理论分析,Al_xGa_(1-x)N薄膜材料的非线性过程主要是双光子吸收主导非线性响应物理过程。实验结果与半导体双光子吸收过程Sheik-Bahae理论符合得很好。

Two-photon Absorption in AlxGa1-xN Films

The ultrafast nonlinear absorption response of GaN and AlxGa1-xN films was studied by employing conventional femto-second Z-scan measurements. In the Z-scan, GaN films exhibit typical two-photon absorption property and with a two-photon absorption coefficient of 3. 5 cm/GW. Simul-taneously, the two-photon absorption coefficient decreases with the increase of the excitation intensi-ty. GaN films possess excellent nonlinear optical property which is dominated by two-or multi-pho-ton absorption. The Z-scan measurement was further used for AlxGa1-xN films with different Al ele-ment content. It is found that the two-photon absorption coefficient of AlxGa1-xN films closely de-pendent on the mole fraction of Al element. The two-photon absorption coefficient decreases from 18 cm/GW to 5 . 6 cm/GW with the increase of Al mole fraction from 0 to 0 . 42 . Considering the con-ventional semiconductor nonlinear absorption theory, it is believed that the observed nonlinear ab-sorption originates from the two-photon absorption dominant nonlinear response. The experimental results are in good agreement with the Sheik-Bahae theoretical prediction for two-photon absorption coefficient.