From the electrical and optical characteristics of AlGaAs vertical cavity surface emitting lasers(VCSELs), the optimum structure of the distributed bragg reflector(DBR) is studied. Using the fabricated VCSELs lasing at 770 nm and 850 nm, the threshold voltage and the L-I curves of the VCSELs are measured as a function of temperature from 160 K to 410 K. Analysing the measured data, the hole barrier height at the Al$_x$Ga$_{1-x}$As/AlAs heterointerface is obtained. It is found that the major portion of the series resistance of 770 nm VCSEL comes from the high potential barrier of the p-side mirror. The contribution of the n-side mirror is found to be negligible compared to that of the p-side mirror. On the other hand, for the 850 nm VCSEL n-mirror contribution is small, but non-negligible. This is because of the nonlinear band gap discontinuity is a function of the difference in the AlAs mole fraction between AlGaAs interfaces making the n-side DBR. Following this analysis the electrical resistance of the n-side DBR could be made small by using Al$_x$Ga$_{1-x}$As layer width x values lager than 0.4. In addition, NOR and INVERTER active optical logic devices using our VCSELs and heterojunction photo-transisters(HPTs) are demonstrated.
