Influence of waveguide strain and surface morphology on AlGaN-based deep UV laser characteristics

Abstract

The waveguide strain and the surface morphologies of AlGaN-based laser heterostructures emitting in the deep UV spectral range have been investigated. In particular, the impact of the AlGaN heterostructure design on the strain relaxation as well as the effect of the growth temperature on the surface morphology were explored. We found strain-induced plastic relaxation for laser heterostructures with 130 nm thick Al0.45Ga0.55N waveguide layers, whereas pseudomorphic growth was obtained for laser heterostructures with Al0.70Ga0.30N waveguide layers. Optically pumped lasing near 280 nm was demonstrated for the coherently grown laser heterostructures. A strong correlation of the surface morphology with the waveguide growth conditions was also observed. Low growth temperatures of 900 °C lead to a high density of V-pits originating from dislocations. By increasing the growth temperatures to 1070 °C the V-pit density significantly decreases, resulting in a more than two-fold reduction of the threshold power density of optically pumped lasers.

Paving the Way for High‐Performance UVB‐LEDs Through Substrate‐Dominated Strain‐Modulation

“…[23][24][25] Simultaneously, the AlGaN underlayer is often relaxed to above 40% to further suppress the compressive strain. [25,26,28] Unfortunately, an excess of AlGaN relaxation onto AlN usually results in some negative effects, including deterioration of the crystalline quality and surface flatness, [31][32][33] which will impair the quality of the subsequent MQWs. In addition, it has been proven that the relaxation of the AlGaN bottom layer will weaken the overlap of electrons and holes in the MQWs, [34] which is not beneficial for the preparation of high luminous efficiency MQWs.…”

Study of AlGaN-based deep ultraviolet laser diodes using one-way step-shaped quantum barriers and symmetrical step-shaped electron and hole blocking layers

“…6,7 However, due to the lattice mismatch and polarization of the electric field, the device still contains serious amounts of carrier leakage along with its weak carrier confinement capabilities and low output power. 8,9 To solve the above problems, Yi et al 10 proposed graded superlattice electron and hole blocking layers to reduce the carrier leakage, Shi et al 11 designed irregular electron and hole blocking layers to improve carrier confinement, and Xing et al 12 proposed a set of convex quantum wells in the multiple-quantum-wells (MQWs) AlGaN-based DUV-LDs to improve the carrier injection efficiency. In addition, Wang et al 13 designed symmetric step-like quantum barriers (QBs) in the single quantum well AlGaN-based DUV-LDs that increased the stimulated emission rate, and Zhang et al 14 changed, in a linear way, the composition of the QB to enable a weakening of the polarization effect and an increase in the injection and recombination of electrons and holes in the active region.…”

“… – 5 In addition, deep ultraviolet laser diodes (DUV-LDs) have been extensively studied and applied because of their small size, light weight, and high-level reliability 6 , 7 . However, due to the lattice mismatch and polarization of the electric field, the device still contains serious amounts of carrier leakage along with its weak carrier confinement capabilities and low output power 8 , 9 …”

Design of AlGaN-based lasers with a buried tunnel junction for sub-300 nm emission

“…Over the last decade or so, a significant amount of research has been devoted towards demonstrating UV-lasers by various research groups [3]. This is mainly because these lasers can enable a number of important and emerging applications including phototherapy in the medical sector [4], water sterilization [5], trace gas sensing [6], polymer curation, indoor plant growth and horticulture, as well as stimulating the formation of anti-cancerogenic substances [7].…”