**2.2 The fabrication process of photonic crystal surface emitting lasers (PCSELs)**

The PhC nanostructure was fabricated on the epitaxial wafers by the following process steps as shown in Fig. 3. In the beginning, the hard mask SiNx 200 nm was deposited on as-grown samples by PECVD. Then, PMMA layer (150 nm) was spun by spinner and exposed by using E-beam writer to form a soft mask. The pattern on the soft mask was transferred to SiNx film to form the hard mask by using ICP-RIE (Oxford Plasmalab system 100), and then, the PMMA layer was removed by dipping ACE. The pattern on hard mask was transferred to GaN by using ICP-RIE (SAMCO RIE-101PH) to form the PhC layer. In order to remove the hard mask, the sample is dipped in BOE. Finally, the PCSEL devices have been fabricated as shown in Fig. 4. Fig. 5. shows the plane-view (a) and the cross section (b) of SEM images of our PCSELs. Although the hole profiles of PhC nanostructure etched through the MQWs region are not perfect due to the lateral plasma etching by ICP-RIE shown in Fig. 5(b), the PhC nanostrustructure near the sample surface which has smooth

Angular-Resolved Optical Characteristics and Threshold

Fig. 5. SEM images of PCSELs: (a) plane view. (b) cross-section view.

**3. Optical measurement system and the foundatment mode of PhC laser**

Section 3.1, the angular-resolved μ-PL (AR μ-PL) system will be introduced, including the pumping lasers, light paths, and so on. Then, using the AR μ-PL system, the characteristics of foundament mode PhC laser would be shown in Section 3.2 and 3.3, such as threshold characteristics and far field patterns, etc. Furthermore, by adopting the multiply scattering method (MSM), the threshold gains of foundamental modes PhC lasers can be calculated in

This section would intorduce the angular-resolved μ-PL (AR μ-PL) system which is designed for multiple applications. As shown in Fig. 6, it can observe two optical pump sources, including a frequency tripled Nd:YVO4 355 nm pulsed laser with a pulse width of ~0.5ns at a repetition rate of 1KHz and 325 nm He-Cd continuous wavelength (CW) laser; two optical pump incidence paths, two collecting PL method and two way to collect sample surface image are as well observed. The samples are pumped by the laser beam with an incident angle from 0 degree to 60 degrees normally from the sample. The laser spot size is about 50 μm in diameter covering the whole PhCs pattern area. The PL spectrum of the samples can be collected by a 15 X objective len and coupled into a spectrometer with a charge-coupled device (Jobin-Yvon iHR320 Spectrometer) or a fiber with a 600 μm core. The resolution is about 0.07 nm for the spectrometer. Fig. 6. shows the setup of the AR μ-PL system. The GaN-based PCSELs were placed in a cryogenics controlled chamber to perform PL experiment at low temperature. The temperature of the chamber can be controlled from room temperature (300 K) down to 77

**(a)**

Section 3.4.

**3.1 Angular-resolved μ-PL (AR μ-PL)** 

K via the liquid nitrogen.

Gain Analysis of GaN-Based 2-D Photonics Crystal Surface Emitting Lasers 7

**(b)**

etching profile show the largest coupling effects of the light field in the MQW region of about 100nm thickness. Therefore the diffraction profiles of PhC nanostructure still can be observed in the following experiment. Besides, the minimun hole diameter and maximum depth of the PhC nanostructure are about 40nm and 1μm, respectively.

Fig. 3. PCSEL fabrication flowcharts: (a) as-grown sample structure, (b) deposit SiNx film by PECVD, (c) spin on PMMA, (d)E-beam lithography, (e) PhC patter transfer to SiNx layer, (f) remove PMMA by Acetone, and (g) PhC patterns transfer to GaN layer.

Fig. 4. The GaN-based PCSEL devices with AlN/GaN DBRs

etching profile show the largest coupling effects of the light field in the MQW region of about 100nm thickness. Therefore the diffraction profiles of PhC nanostructure still can be observed in the following experiment. Besides, the minimun hole diameter and maximum

Fig. 3. PCSEL fabrication flowcharts: (a) as-grown sample structure, (b) deposit SiNx film by PECVD, (c) spin on PMMA, (d)E-beam lithography, (e) PhC patter transfer to SiNx layer, (f)

remove PMMA by Acetone, and (g) PhC patterns transfer to GaN layer.

Fig. 4. The GaN-based PCSEL devices with AlN/GaN DBRs

depth of the PhC nanostructure are about 40nm and 1μm, respectively.

Fig. 5. SEM images of PCSELs: (a) plane view. (b) cross-section view.
