Si homojunction structured near-infrared laser based on a phonon-assisted process

Abstract

We fabricated several near-infrared Si laser devices (wavelength ∼1300 nm) showing continuous-wave oscillation at room temperature by using a phonon-assisted process induced by dressed photons. Their optical resonators were formed of ridge waveguides with a width of 10 µm and a thickness of 2 µm, with two cleaved facets, and the resonator lengths were 250-1000 µm. The oscillation threshold currents of these Si lasers were 50-60 mA. From near-field and far-field images of the optical radiation pattern, we observed the high directivity which is characteristic of a laser beam. Typical values of the threshold current density for laser oscillation, the ratio of powers in the TE polarization and TM polarization during oscillation, the optical output power at a current of 60 mA, and the external differential quantum efficiency were 1.1-2.0 kA/cm 2 , 8:1, 50 µW, and 1 %, respectively.Because silicon (Si) is an indirect-transition-type semiconductor, it is difficult to use it as a material for optical devices To solve these problems, in the research described here, we developed a Si laser showing continuous-wave operation at room temperature. To do so, we applied the same fabrication method and operating principle used for a Si-LED that we previously developed, which used a Si crystal having a p-n homojunction [4]. We report the results here.Similar to the fabrication of Si LEDs that we have already reported, in this work, first we formed a p-n homojunction by introducing a p dopant into an n-type Si substrate by ion implantation. Then, while irradiating the structure with light, we applied an electrical current to generate Joule heating, causing annealing. Stimulated emission was produced via a two-step transition process driven by the light irradiation. This process is described below [4,5].(i) First step: Dressed photons are generated by the light irradiation in regions where the dopant concentration in the p-n junction has a non-uniform spatial distribution. A dressed photon is a quasi-particle representing a coupled state due to the mutual interaction between a photon and an electron on the nanometer scale. The dressed photon then couples with a multi-mode phonon, generating stimulated emission that causes a conduction-band electron to transition from an initial state |E ex ; el ⊗ |E ex thermal ; phonon to an intermediate state |E g ; el ⊗ |E ex ; phonon . Here, |E ex ; el and |E g ; el respectively represent the excited state (conduction band) and ground state (valence band) of the

Increasing Si photodetector photosensitivity in near-infrared region and manifestation of optical amplification by dressed photons

“…The above method is the same as the method of fabricating Si-LEDs previously reported by the authors [14,15]. Here, however, in order to make use of the stimulated emission process described in Sect.…”

“…We applied the same fabrication method and light emission principle of a silicon light emitting diode (Si-LED) based on a phonon-assisted process that we previously proposed [14,15]. Specifically, while radiating light, Joule-heat annealing was performed to control the spatial distribution of the impurity (boron) concentration in a Si crystal in a self-organized manner, to efficiently generate dressed photons.…”

Decreasing the threshold current density in Si lasers fabricated by using dressed-photons

“…After above annealing method, laser oscillation occurs when forward current is applied to this device. The photon energy of this device's laser oscillation was as high as that of the laser light used for annealing because the highest probability of stimulated emission was obtained at the photon energy of the annealing light [6]. The stimulated emission occurred via a two-step transition, which is explained in [10] as stimulated emission process (1") and (2").…”

“…Therefore, when evaluating the differential gain coefficient g ′ , the edge of the light waveguide is illuminated with laser light, and the emitted light, which reflects amplification or absorption in the light waveguide, is measured from the other edge as a function of the current density [16]. However, the same measuring method cannot be adopted for this laser [6], such as one made from Si, because the photon energy of the light emitted from the Si laser in this research was 0.94 eV (wavelength, 1.32 µm), which is less than the bandgap energy of Si, and thus this light cannot be absorbed by a Si crystal.…”

“…We have succeeded in developing a near-infrared Si laser that oscillated continuously at room temperature via current injection [6]. This Si laser was made of bulk Si and was based on the principle of dressed-photons.…”