The fabrication and lasing characteristics of oxide-confined 795 nm VCSELs with close and open isolation trenches

In this paper, 795 nm vertical cavity surface emitting lasers (VCSELs) with close and open isolation trench structures have been designed and produced. An Al₂O₃ aperture with a diameter of 4 µm was formed by oxidizing the AlAs layer to confine the current and lateral optical mode. The characteristics of the VCSEL based on Al_0.07Ga_0.93As/Al_0.35Ga_0.65As multiple quantum wells (MQWs) under continuous wave operation show that the VCSEL with close isolation trench structure has a threshold current of about 1.5 mA and a maximum optical output power of 0.35 mW, and it exhibits a single mode operation below 3.5 mA. However, the VCSEL with an open isolation trench structure shows a much larger threshold current of 6 mA due to a current leakage through the connecting and surrounding area and more high order modes will be incurred by increasing the driving current. The simplification of the fabrication process of the VCSELs with open isolation trenches is obtained at the cost of poor performance. By introducing strain in the MQWs, the Al_0.15Ga_0.75In_0.1As/Al_0.4Ga_0.6As MQWs based VCSEL with close isolation trench structure exhibits a threshold current as low as 0.42 mA.