Elevated-oxide VCSELs of which spacing between the 1-lambda cavity and oxide layer is greater than the conventional ones are designed, fabricated and characterized in order to achieve wide single-mode operation, stable turn-off performance, superior electro-static discharge (ESD) resistivity and reliability.
Elevated-oxide VCSELs… structures are optimized using one-dimensional transfer matrix method combined with three-dimensional electro-thermal model, and compared with measured results. Also, the structure parameters such as metal and oxide aperture radii are optimized.
Temperature dependent static and dynamic characteristics the elevated-oxide VCSELs are competent compared with conventional oxide VCSELs in terms of single-mode performance, turn-off characteristics and resistivity to ESD exposure. The single-mode operation range of the elevated-oxide-layer VCSELs is wider due to the smaller current confinement and optical confinement.
The dynamic characteristics, particularly, turn-off characteristics of the elevated-oxide VCSELs are investigated. The turn-off-induced anomalies such as off-state turn-on and tails of the conventional and elevated-oxide VCSELs are extracted from the turn-off transient responses, and compared. Also, temperature dependence of the turn-off-induced anomalies is investigated. The optimum vertical position of the oxide layer and the oxide aperture diameter for high turn-off performance are proposed. With the optimum structure parameters, suppression of the turn-off-induced anomalies causing significant increases in timing jitter is achieved.
Forward and reverse ESD-induced degradation behavior of the conventional oxide VCSELs is also investigated. Both the forward and reverse ESD-induced degradation incurred increase in the leakage current, threshold current and series resistance simultaneously with the decrease in the slope efficiency and effective active area. However, the reverse ESD causes more sudden and abrupt degradation than that of the forward ESD pulses due to the low reverse breakdown voltage. The structure dependent ESD damage threshold of four different types of elevated-oxide VCSELs shows that the elevated-oxide VCSELs are more robust to ESD damage than conventional oxide VCSELs due to reduced oxide-induced stress.
