The Influence of Zn-Diffusion Depth on the Static and Dynamic Behavior of Zn-Diffusion High-Speed Vertical-Cavity Surface-Emitting Lasers at an 850 nm Wavelength

We studied the static and dynamic performance of high-speed Zn-diffusion vertical-cavity surface-emitting lasers (VCSELs) (at an 850-nm optical wavelength) as affected by different Zn-diffusion depths. Device A has the largest Zn-diffusion depth $({\sim}1.3\ \mu{\hbox {m}})$ and can sustain single-mode operations under a whole range of bias currents, exhibiting the largest differential quantum efficiency and smallest far-field divergence angle. Devices B and C have smaller Zn-diffusion depths (0.5 $\mu{\hbox {m}}$ for device B and 0 $\mu{\hbox {m}}$ for device C) and exhibit poorer multimode performance. However, due to the serious spatial hole burning effect of device A, induced by its single-spot and high-power output, the measured electrical-to-optical (EO) frequency response of device A shows a more serious ( $>$3 dB) low-frequency ( $≪$2 GHz) rolloff than does that of the other two devices. Although device B (with a shallow Zn-diffusion depth) shows multimode performance, with it we can minimize the low-frequency roll-off problem, due to its more uniform photon density distribution and less spatial-hole burning effect than that of device A. Using device B, we can achieve an 11-GHz 3-dB bandwidth, the highest modulation current efficiency $({\sim}8\ \hbox{GHz/mA}^{1/2})$, and clear eye-opening at 10 Gb/s operation, with the lowest dc and radio frequency power consumption among the three devices. These measurement results indicate that the dynamic and static performance of high-speed VCSELs can be optimized by controlling the Zn-diffusion depth, and manipulating the number of optical modes in the VCSEL cavity.