Effect of Laser Pulse Width and Intensity Distribution on the Crystallographic Characteristics of GeSn Film

Abstract

Germanium-tin (GeSn) alloy is considered a promising candidate for a Si-based short-wavelength infrared range (SWIR) detector and laser source due to its excellent carrier mobility and bandgap tunability. Pulsed laser annealing (PLA) is one of the preeminent methods for preparing GeSn crystal films with high Sn content. However, current reports have not systematically investigated the effect of different pulse-width lasers on the crystalline quality of GeSn films. In addition, the intensity of the spot follows the gaussian distribution. As a result, various regions would have different crystalline properties. Therefore, in this study, we first provide the Raman spectra of several feature regions in the ablation state for single spot processing with various pulse-width lasers (continuous-wave, nanosecond, femtosecond). Furthermore, the impact of laser pulse width on the crystallization characteristics of GeSn film is explored for different single-spot processing states, particularly the Sn content incorporated into GeSn crystals. The transient heating time of the film surface and the faster non-equilibrium transition of the surface temperature inhibit the segregation of the Sn component. By comparing the Raman spectra of the pulsed laser, the continuous-wave laser shows the most acute Sn segregation phenomenon, with the lowest Sn content of approximately 2%. However, the femtosecond laser both ensures crystallization of the film and effective suppression of Sn expulsion from the lattices, and the content of Sn is 8.07%, which is similar to the origin of GeSn film.