Deep-UV distributed Bragg reflectors (DBRs) operating at λ = 220–250 nm with reflectivity close to unity were produced using epitaxial AlxGa1-xN/AlN superlattice structures grown on AlN/sapphire templates via metalorganic chemical vapor deposition. Owing to the near-bandedge excitonic resonance in the AlxGa1-xN layers, the AlN mole fractions, x, were regulated to keep the reflective plateau within the enhanced refractive index contrast region between AlGaN and AlN of approximately 7%–11%. For DBRs incorporating high-index layers of AlGaN grown via a flow-rate modulated epitaxy technique, a reflectivity of 97% was achieved with a total pair number of 30.5 which was much smaller than number of pairs needed for the DBRs with conventionally grown AlGaN layers. The stopbands of these DBRs were about 6–9 nm.

An optically pumped vertical-cavity surface-emitting laser with an electrically conducting n-type distributed Bragg reflector was achieved at 374.9 nm. An epitaxially grown 40-pair n-type AlGaN/GaN distributed Bragg reflector was used as the bottom mirror, while the top mirror was formed by a dielectric distributed Bragg reflector composed of seven pairs of HfO2/SiO2. A numerical simulation for the optical mode clearly demonstrated that a high confinement factor was achieved and the threshold pumping power density at room temperature was measured as 1.64 MW/cm2. The achieved optically pumped laser demonstrates the potential of utilizing an n-type distributed Bragg reflector for surface-emitting optical devices.

We report the crack-free growth of a 45-pair Al0.30Ga0.70N/Al0.04Ga0.96N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al0.30Ga0.70N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al0.04Ga0.96N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al0.30Ga0.70N/Al0.04Ga0.96N DBR was able to be grown with an atomically smooth surface morphology. Smooth surfaces and sharp interfaces were observed throughout the structure using high-angle annular dark-field imaging in the STEM. The 45-pair AlGaN-based DBR provided a peak reflectivity of 95.4% at λ = 368 nm with a bandwidth of 15 nm.

We report an electrically conducting 40-pair silicon doped Al 0.12 Ga 0.88 N/GaN distributed Bragg reflector (DBR) grown by metalorganic chemical vapor deposition on a silicon doped n-type GaN template. Due to the relatively small lattice mismatch between AlGaN and GaN, strain managing layers are not required for crack-free n-DBR growth. The DBR demonstrates a peak reflectivity of 91.6% at 368 nm with stopband of 11 nm. In addition, the 40-pair n-DBR shows the vertical resistance of 5.5 Ω, which corresponds to bulk resistivity of 0.52 Ωcm, near the maximum measured current of 100 mA. Keywords:A3. Metalorganic chemical vapor deposition B1. Nitride B2. Semiconductor III-V material B3. Laser diodes PACS #: 42.55.Px Semiconductor lasers, solid-state lasers 78.66.Fd Optical properties of specific thin films, III-V semiconductors 81.15.Gh Methods of deposition of films and coatings; film growth and epitaxy, Chemical vapor deposition including plasma-enhanced CVD, MOCVD, etc. a) Also

In this study, we employed bulk (0001) AlN substrates for the metalorganic chemical vapor deposition growth of AlGaN multi‐quantum‐well heterostructures in an Aixtron 6 × 2″ close‐coupled showerhead reactor. The wafers were fabricated into cleaved bars with a cavity length of ∼1 mm. Two different layer structure designs are presented in this work. Both laser bars were optically pumped by a pulsed 193 nm ArF excimer laser at room temperature. The lasing wavelengths are 243.5 nm and 245.3 nm with threshold power density 427 kW/cm2 and 297 kW/cm2, respectively. Both laser bars showed transverse electric‐polarization‐dominated optical emission when operating above threshold. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)