Surface states generally degrade semiconductor device performance by raising the charge injection barrier height, introducing localized trap states, inducing surface leakage current, and altering the electric potential. We show that the giant built-in electric field created by the surface states can be harnessed to enable passive wavelength conversion without utilizing any nonlinear optical phenomena. Photo-excited surface plasmons are coupled to the surface states to generate an electron gas, which is routed to a nanoantenna array through the giant electric field created by the surface states. The induced current on the nanoantennas, which contains mixing product of different optical frequency components, generates radiation at the beat frequencies of the incident photons. We utilize the functionalities of plasmon-coupled surface states to demonstrate passive wavelength conversion of nanojoule optical pulses at a 1550 nm center wavelength to terahertz regime with efficiencies that exceed nonlinear optical methods by 4-orders of magnitude.

表面状态通常会通过提高电荷注入势垒高度、引入局部陷阱状态、诱导表面漏电流和改变电势来降低半导体器件的性能。我们表明，可以利用由表面状态产生的巨大内置电场来实现无源波长转换，而无需利用任何非线性光学现象。光激发表面等离子激元与表面态耦合以产生电子气，该电子气通过表面态产生的巨大电场路由到纳米天线阵列。纳米天线上的感应电流包含不同光学频率分量的混合产物，以入射光子的拍频产生辐射。