由於氮化鎵藍紫光垂直共振腔面射型雷射之晶圓片製作不易，容易造成低增益及高損耗的現象，因此本實驗採用不同於常見的氧化物侷限結構，利用矽擴散反轉p-GaN為n-GaN製作出擴散型侷限結構，藉此定義出電流侷限範圍，期望能更有效的將電流集中提高增益並且降低閥值電流。
本實驗結果顯示擴散型侷限結構確實能有效的將電流侷限，並且提高增益，增加受激放射(stimulated emission)。由發光頻譜來看，製程所形成的共振腔結構確實已能將發光頻譜主峰的半高寬收窄至2nm，但峰值波長幾乎都落在磊晶式DBR禁止帶的邊緣處，存在二或三個波峰在競爭，主峰與次峰的峰值比(side mode suppression ratio)最高達到約5倍，但在元件產生熱衰竭效應前皆無觀察到雷射現象。
雖然並無產生雷射，但透過變角度電致發光量測的遠場光分佈圖結果得知元件指向性確實較一般無共振腔元件來的良好，遠場光分佈圖的半功率角(half power angle)為30°左右，且峰值波長隨著量測角度增大而有明顯規律的藍移的現象，顯示共振腔仍有發揮一定作用。

It is difficult to grow high-quality epitaxial DBRs for GaN-based vertical-cavity surface-emitting lasers (VCSELs) resulting in VCSEL materials of low gain and high loss. Therefore we replaced the general silicon-oxide/silicon-nitride insulating layers with Si diffusion-defined confinement structure to enhance the current confinement. Si diffusion in p-GaN was used to convert p-GaN into n-GaN that formed a 3D current-blocking structure. Hopefully the VCSELs with this structure will have good performance in terms of threshold current and optical output power.

The experimental results demonstrated that Si diffusion-defined confinement structure effectively confined the current path to increase the gain of the diode and the probability of stimulated emission. From the emission spectra at various current levels, we observed the full width at half maximum (FWHM) of the primary emission peak was reduced to below 2nm, and there were two or three resonant-cavity modes competing for the gain. The largest side mode suppression ratio obtained was 5. And we found almost all the primary peak wavelengths were located at the edge of the stop band of the bottom DBR.

Unfortunately we didn’t observe lasing while operating diodes up to 20mA in current. But the far-field pattern exhibited a half power angle of about 30°, which was much smaller than the 60° of the Lambertian radiation pattern observed in LEDs. Moreover, from angle-resolved emission spectra, we observed off-axial resonant modes of which the peak wavelengths blue-shifted regularly with increasing angle. These characteristics indicated these devices have strong resonant cavity effect.

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