Optical gain in group-III nitrides

Precision Experiments

Nitrides-based (GaN, AlN and InN and their alloys) semiconductors have been recognized as one of the most promising materials for realizing optical devices. These compounds were selected not only due to their wide direct energy gap but also due to their excellent physical properties such as e.g. hardness, physical and chemical stability etc. InGaN-based violet and blue laser diodes show high output power and low threshold current. They are already commercially available in a wide field of applications. However, if the emission wavelegth is extended towards the green spectral range, device performance of InGaN laser diodes is strongly decreased. The phd research focus on investigation of the limiting factors of optical gain for long-wave (green and beyond) InGaN/GaN-based light emitting laser diodes (LD). In this context the most important questions are: What are the limiting factors: the impact of defects (e.g. threading or/and misfit dislocations, point defects) and therefore the non-radiative recombination processes on optical gain and/or the influence of the optical confinement properties on optical gain. For this purpose we carry out optical gain measurements by using the variable stripe length method (VSLM) on laser structures grown on different substrates (sapphire and GaN bulk) with various orientations (c- as well non- and semipolar plane), in which several parameters such as number and thickness of quantum well, cladding layers (AlGaN, AlInN) as well as indium content were varied.

TU Braunschweig
Ph.D. student: