Selective oxidation of AlGaAs/GaAs structure and its application to vertical cavity lasers

We report on vertical-cavity surface-emitting lasers (VCSELs) fabricated using selective oxidation to form a current aperture and an oxide surface barrier to seal buried AlAs layers in distributed Bragg reflectors. The lateral selective oxidation of the AlAs layer is strongly influenced by its thickness and heterointerface structures. The oxidation rate decreases rapidly with decreasing AlAs thickness in the range of < 80 nm, and the presence of AlGaAs layers on both sides of the AlAs layer reduces the oxidation rate. In addition, an oxide surface barrier with a thickness of ∼1 μm is formed by a brief wet oxidation which blocks diffusing oxygen species during the second wet oxidation. The effectiveness of the seal is demonstrated by using the oxide barrier as a mask against wet oxidation in the fabrication of oxide-confined VCSELs. The 8×8 μm² devices with three quantum wells exhibit a threshold current of 400 μA, and the 4×4 μm² single-quantum devices possess a threshold current as low as 85 μA.