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In this paper, we discuss experimental results and the potential for improvement of blue and green laser diode (LD) performance by using semipolar substrates. We show that the InGaN quantum well (QW) grown on a semipolar plane allows higher characteristic temperature, T 0 , and higher optical gain, which are important for improving laser efficiency, thanks to its unique electronic spectrum properties. Epitaxial structure growth benefits from the wider process window for certain orientations. At the same time it is associated with a risk of strain relaxation, which can be addressed by appropriate strain relaxation management and/or strain balancing of waveguide core.

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.

We studied characteristic temperatures (T0) of laser diodes (LDs) grown on semipolar GaN substrates and emitting in the green spectral range. For several semipolar laser designs with and without an electron blocking layer (EBL), T0 remains higher (161–246 K) than that typically reported for c-plane green LDs. The slope efficiency measured in the pulsed regime is nearly temperature independent. These observations indicate that T0 is mainly determined by intrinsic quantum well (QW) properties, such as higher differential gain. A high T0 and a sufficient injection efficiency allow the achievement of a continuous wave output power of 60 mW for an LD without an EBL.

Phone: þ1 607 974 2835, Fax: þ1 607 974 1650Using varied stripe length method we systematically studied optical gain properties of blue-green 3 nm InGaN QWs grown on c-plane and (11À22) semipolar substrates. We determined that for such structures when the product of modal net gain at peak and stripe length exceeds factor 5 the gain saturation occurs due to depletion of pumped carriers. We then focused our attention on the gain in unsaturated conditions. We observed strong gain peak position blue shift with increase of pumping power for both substrate orientations due to quantum well state filling and for c-plane due to piezoelectric field screening. Thus in order to increase lasing wavelength, minimizing optical losses, and maximizing modal gain are essential. We then found that for the semipolar QWs the gain at $500 nm was 2Â higher with the stripe along [À1À123] direction despite the fact that at low pumping level the polarization switching of spontaneous emission resulted predominant Ejj[À1À123]. Finally we compared the semipolar and c-plane QWs and found that the gain increase with pumping power of c-plane QW is slower than that for semipolar QW in high gain direction while the transparency pumping power is lower for c-plane.