Indistinct Threshold Laser Operation in a pnpn Vertical to Surface Transmission Electrophotonic Device with a Vertical Cavity

We demonstrate indistinct threshold pulsed laser operation in a pnpn vertical to surface transmission electro-photonic device with a vertical cavity. The proposed structure has a laser cavity covered with plated gold, which has high reflectivity, and the laser light is emitted from the distributed Bragg reflector (DBR) with no gold. Because of this, spontaneous emission remains in the laser cavity and does not go out from the laser cavity. As a result, spontaneous emission is absorbed and the carriers are regenerated. That is, the injected carriers are converted to light and spontaneous emission is reconverted to carriers. Due to this effect (photon recycling), threshold current density decreases and indistinct threshold laser operation is obtained. In the indistinct threshold operation, the light output is linearly polarized. Also, submode suppression ratio is larger than 25 dB and the divergence angle of a far field is as narrow as 6.8°. These indistinct threshold laser characteristics lead to high slope efficiency in low current level. To achieve high slope efficiency in the overall current level, DBR mirrors are designed and high slope efficiency of 0.32 mW/mA is obtained.