Jerome Napierala

500-nm Optical Gain Anisotropy of Semipolar (1122) InGaN Quantum Wells

We studied the effect of carrier population on light emission polarization of green InGaN quantum wells (QWs) on the semipolar (1122) plane. The 3 nm thick QWs emitting light at about 540 nm at low pumping power have electrical field (E) component E∥[1123] stronger than that E∥[1100]. However, we found that increasing the pumping power changed the sign of the polarization ratio. Using the varied stripe length (VSL) method, we measured the optical gain for light propagating ∥[1123] direction to be ~2 times that of light propagating ∥[1100] direction. We explain this behavior by inhomogeneous QW state filling.

Impact of Carrier Transport on Aquamarine-Green Laser Performance

We studied the carrier transport phenomena of the multiple-quantum-well (MQW) active region and their impact on the performance of aquamarine and green laser diodes (LDs) grown on polar and semipolar planes. The ballistic carrier transport mechanism was found to be dominant in the MQW region. For the c-plane, because of the high hole capture probability and slow escape rate, mainly the quantum wells (QWs) positioned close to the p-side are electrically pumped. The optical loss induced by the underpumped QWs further away from the p-side leads to significantly higher laser threshold current density and a longer lasing wavelength with increased number of QWs. These effects are not significant for semipolar LD structures.

Lasing and optical gain around 500 nm from optically pumped lasers grown on c -plane GaN substrates

Using the variable stripe length method we demonstrated positive net optical gain around 500 nm for an optically pumped laser with InGaN/GaN multiple quantum wells grown on c-plane freestanding GaN substrates. We found that owing to low optical gain, reducing optical losses is crucial to increasing lasing wavelength. We demonstrated lasing at 502 nm by using a 3-mm-long cavity with cleaved facets.