True green InGaN laser diodes

Abstract

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 À1 . Mounted InGaNbased 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.

Origin of predominantly a type dislocations in InGaN layers and wells grown on (0001) GaN

“…For example, green laser diodes at 515 nm and 520 nm in either pulse or continuous-wave operation at room temperature have been realized based on growth improvements for higher quality of InGaN quantum wells. [32][33][34] Such devices would not have operated properly without reducing the dislocation density through the active regions to an acceptable level. In fact, a factor of 10 defect reduction has been estimated based on the performance of the laser diodes.…”

III-Nitride Light-Emitting Devices

“…A summary plot of threshold current density vs. the lasing threshold of reported nitride LDs illustrates this point (shown in Figure 9b). In spite of the abovementioned challenges, significant developments have been made with green (515-535 nm) LDs since their early development in 2009-2013 [195,196,[201][202][203]. The first watt-class green laser, with an emission wavelength of 520 nm, was reported by Nichia on a conventional c-plane GaN substrate in 2012 [204].…”

Interdependency of surface morphology and wavelength fluctuations of indium‐rich InGaN/GaN quantum wells

“…One of the main challenges is to grow indium‐rich InGaN layers with good crystal quality 1. Homogeneous indium incorporation in the ternary InGaN QW layer is a key parameter to obtain highest peak gain and best laser results 2–4. Hence, it is necessary to gain a better understanding of InGaN growth mechanisms to optimize the QW growth to reach highest uniformity and lowest defect density.…”