Stimulated Smith-Purcell semiconductor THz sources

Abstract

We propose a novel room-temperature semiconductor source of narrowband coherent THz radiation that radiates via the Smith-Purcell effect and uses the Gunn effect to increase the radiated power (Figure 1). The radiation frequency of the device depends only on the grating period and the velocity of the Gunn domain, reaching low THz range with submicron grating. The Smith-Purcell effect is well-known in vacuum electronics and accelerator physics: a DC electron beam focused parallel to a metallic grating generates weak, incoherent electromagnetic radiation called spontaneous Smith-Purcell radiation (SPR). A bunched electron beam instead generates coherent stimulated SPR, with radiated power many orders of magnitude stronger than spontaneous SPR. Spontaneous SPR has been observed in semiconductors, but only at low temperature. The Gunn effect naturally provides space-charge bunching in semiconductors, and Gunn domains generate stimulated SPR at room temperature in the proposed devices. We develop a simple analytic model to describe the radiation which agrees well with device simulations. The small size of the radiative portion of the device suggests the use of an integrated antenna which significantly boosts the power of simulated devices. Our results indicate that the effect should be observable from a InP device, with power density of 30nW/μm of device width at 0.27 THz and 6nW/μm at 0.44THz. Results based on InN parameters look very promising for this approach with calculated power densities of 3.5μW/μm at 0.25THz, 20nW/μm at 1.0THz, and 3nW/μm at 2.0THz. We conclude that experimental investigation is warranted.