Fabrication and characteristics of a GaN-based microcavity laser with shallow etched mesa Ying-Yu Lai, Yu-Hsun Chou, Yu-Sheng Wu, Yu-Pin Lan, Tien-Chang Lu*, and Shing-Chung Wang Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan E-mail: timtclu@mail.nctu.edu.tw Received April 15, 2014; accepted April 21, 2014; published online May 14, 2014 In this work, we have developed a simple GaN-based microcavity (MC) with an intracavity shallow etched mesa. The textured GaN-based MC incorporated two high-reflectivity dielectric Bragg mirrors and an InGaN/GaN multiple quantum well with a shallow etched mesa as an optical confined structure. Lasing and transverse optical confinement characteristics have been verified by measuring devices with different mesa diameters. A quality factor (Q) of 2600 and a threshold energy of 30 nJ have been observed in a 10-μm-diameter device. Such a cavity structure could be implanted into electrically pumped GaN vertical-cavity surface-emitting lasers for supporting efficient transverse confinement. © 2014 The Japan Society of Applied Physics P lanar microcavities (MCs) embedded with a semi- conductor active layer have been utilized in various optoelectronic applications, especially laser devices. A typical example is the vertical-cavity surface-emitting lasers (VCSELs), which are driven by photonic stimulated emission. 1) As the active layer exhibits a strong excitonic feature, the MC could enter into the strong coupled polaritonic regime through strong exciton–photon coupling and achieve an ultralow-threshold polariton laser through the polaritonic stimulated scattering. 2) Among so many semi- conductor materials, GaN and its ternary and quaternary alloys are regarded as the most popular material systems for novel MC polaritonic emitters and vertical-cavity laser devices owing to their large exciton binding energy (³26 meV) and wide spectral tuning range in the ultra- violet–visible region. 3,4) Generally, the GaN-based MCs could be divided into three major types from their distributed Bragg reflector (DBR) compositions: all-epitaxial, epitaxial- dielectric hybrid, and all-dielectric. 5–11) So far, the optically pumped polariton lasers, electrically pumped VCSELs, and polariton LEDs have been demonstrated using planar GaN-based hybrid MCs. 12–14) However, the efficient lateral optical confinement among these devices is still lacking and limiting their performance. In 2011, Cheng et al. successfully achieved a high-quality-factor (Q) MC light emitter with sufficient lateral optical/electrical confinement using an intracavity AlN aperture. 15) Unfortunately, the insertion of AlN apertures may cause additional unexpected damage to the multiple quantum well (MQW) owing to their higher regrowth temperature. In the GaAs system, the lateral optical confinement could be easily achieved using an etched micro- pillar or a micropillar embedded into BCB. 16,17) However, it is hard to etch down a whole GaN micropillar cavity owing to the difficult etching process of the III–nitride system. In view of this, the surface-textured structure would be a better way to introduce a sufficiently large index contrast for lateral optical confinement without causing damage to the gain medium in the VCSELs or MC devices. Such a technique has recently been demonstrated in an electrically pumped GaAs MC emitter for tailoring the three-dimensional photonic confinement, but has not yet been reported in the GaN-based MC system. 18) In this letter, we demonstrate a GaN-based all-dielectric MC with in-plane optical confinement using a shallow etched mesa structure. The all-dielectric MC provides a wide range of high-reflectivity stopbands for flexibility in the fabrication process. The shallow etched mesa structure presents a sufficient lateral optical confinement owing to its higher effective refractive index. The multi-transverse mode spectra show the lateral confinement of the proposed shallow etched mesa structure. In addition, the device with a larger mesa diameter has a higher Q value and a lower threshold density owing to its smaller diffraction loss and scattering loss. Figure 1(a) shows the schematic diagram of the proposed textured GaN-based MC. The original cavity layers were grown by metal organic chemical vapor deposition (MOCVD) on a (0001) c-plane sapphire substrate, followed by a 30 nm GaN nucleation layer at 500 °C, a 2 μm undoped GaN (u-GaN) spacer at 1100 °C, a 2 μm n-GaN layer, 10 pairs of In 0.1 Ga 0.9 N (2 nm)/GaN (10 nm) MQWs, and a 150 nm p-GaN spacer. An 11.5-pair TiO 2 /SiO 2 DBR was depo- sited on top of the p-GaN spacer using an E-gun deposition (a) (b) (c) Fig. 1. (a) Schematic diagram of textured GaN-based MC structure and corresponding effective refractive index distribution. (b) A 10 © 10 μm 2 AFM scan of an n-GaN surface after polishing. (c) Scanning electron microscopy (SEM) image of textured mesa on n-GaN surface. Applied Physics Express 7, 062101 (2014) http://dx.doi.org/10.7567/APEX.7.062101 062101-1 © 2014 The Japan Society of Applied Physics