Fig. 1. Schematic diagrams for (a) the conventional InGaN/GaN VCSEL and (b) the InGaN/GaN VCSEL with a p-AlGaN/p-GaN structured p-type hole injection layer, in which polarization induced sheet charges exist at the p-AlGaN/p-GaN interface. The φ₁ and φ₂ denote the barrier heights at p-EBL/p-GaN and p-EBL/p-AlGaN interfaces, respectively.

Fig. 2. (a) Hole concentration profiles in the MQWs region, (b) lateral distribution of hole concentration, and (c) hole injection current for VCSELs A and B1 to B3 at 20 mA. (d) Laser power and applied voltage in terms of the injection current for VCSELs A and B1 to B3.

Fig. 3. (a) Electric field profiles in the p-Al_xGa_1-xN and p-GaN layers for VCSELs A, B1, B2, and B3, (b) hole concentration profiles in the p-EBL, p-Al_xGa_1-xN, and p-GaN layers for VCSELs A, B1, B2, and B3, respectively. Data are calculated at the current of 20 mA.

Fig. 4. Valence band profiles in the p-EBL and the p-AlGaN layers for (a) VCSEL A, (b) VCSEL B1, (c) VCSEL B2, and (d) VCSEL B3. Data are calculated at the current of 20 mA.

Fig. 5. Calculated small-signal modulation response at the current levels of (a) 1 mA and (b) 20 mA for VCSELs A, B1, B2, and B3. Stimulated radiative recombination rate (R_sti) in the MQWs at the currents of (c) 1 mA and (d) 20 mA for VCSELs A, B1, B2, and B3. Insets of (a) and (b) show 3 dB frequency bandwidth at the currents of 1 mA and 20 mA, respectively.

Table 1. Different AlN Compositions of the p-AlxGa1−xN Layer for VCSELs B1 to B3