Here, we report the cw laser operation of electrically pumped GaN-based vertical cavity surface emitting laser (VCSEL). The GaN-based VCSEL has a ten-pair InGaN∕GaN multiple quantum well active layer embedded in a GaN hybrid microcavity of 5λ optical thickness with two high reflectivity mirrors provided by an epitaxially grown AlN∕GaN distributed Bragg reflector (DBR) and a Ta2O5∕SiO2 dielectric DBR. cw laser action was achieved at a threshold injection current of 1.4mA at 77K. The laser emitted a blue wavelength at 462nm with a narrow linewidth of about 0.15nm. The laser beam has a divergence angle of about 11.7° with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5×10−2 was measured.

A crack-free GaN∕AlN distributed Bragg reflector (DBR) incorporated with GaN∕AlN superlattice (SL) layers was grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition. Three sets of half-wave layers consisting of 5.5 periods of GaN∕AlN SL layers and GaN layer were inserted in every five pairs of the 20 pair GaN∕AlN DBR structure to suppress the crack generation. The grown GaN∕AlN DBRs with SL insertion layers showed no observable cracks in the structure and achieved high peak reflectivity of 97% at 399nm with a stop band width of 14nm. Based on the x-ray analysis, the reduction in the in-plane tensile stress in the DBR structure with insertion of SL layers could be responsible for the suppression of crack formation and achievement of high reflectivity.

We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AlN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta 2 O 5 /SiO 2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed by Ta 2 O 5 /SiO 2 and TiO 2 /SiO 2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10 À2. In addition, a high characteristic temperature of over 240 K was measured, and a distinct spatially inhomogeneous emission pattern was observed.

We report the growth over 2 inch sapphire substrates of hybrid nitride‐based microcavities using one crack‐free highly reflective AlN/GaN distributed Bragg reflectors (DBRs) incorporated with AlN/GaN superlattice (SL) insertion layers and Ta2O5/SiO2 DBRs. The optical cavity is formed by a 5λ cavity consisting of n‐type GaN, 10 pairs multiple quantum wells and p‐type GaN sandwiched by AlN/GaN and Ta2O5/SiO2 DBRs. Reflectivity and photoluminescence measurements were carried out on these structures. A 29 periods AlN/GaN DBR incorporated with six AlN/GaN superlattice insertion layers showed no observable cracks and achieved a peak reflectivity of 99.4% and a stopband of 21 nm. Based on these high quality DBRs, the cavity mode is clearly resolved with a linewidth of 2.6 nm. These results demonstrate that the AlN/GaN system is very promising for the achievement of strong light–matter interaction and the fabrication of nitride‐based vertical cavity surface emitting lasers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)