True green InGaN laser diodes

We present true green InGaN ridge waveguide (RWG) laser diodes (LDs) at 520 nm on c-plane GaN substrates in pulse operation at room temperature. Defect reduction in the In-rich quantum wells by improving growth conditions of the epitaxial layers is the key parameter to demonstrate laser operation at this wavelength. Carrier lifetime measurements in combination with electroluminescence (EL) data and simulations of competing recombination processes below laser threshold confirm that the reduction of defects in the light emitting InGaN quantum wells is essential to realize true green nitride-based LDs with low laser threshold of 125 mA and good slope efficiency of 220 mW/A for optical output power level up to 50 mW. Investigation of the lateral far field of 520 nm RWG LDs shows a perfect beam quality. The measured vertical far field shows a substrate mode due to leakage into the transparent GaN substrate supported by waveguide simulations with an additional internal loss of less than 1 cm(-1). Mounted InGaN-based ridge LDs at 500 nm demonstrate high optical output power of 35 mW in cw operation with good wall plug efficiency of 3.5% at room temperature. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim