To improve the optical output power intensity of the visible AlGaAs LED with double heterostructure, the various methods were studied.
At first, it was needed to reduce the defects which was introduced during the LPE process. As a possible method, the turbo molecular pump was installed to the LPE system. By this, the graphite boat could be undergone high temperature baking at 900℃ for 50hr with the vacuum of less than $1\times10^{-5}$ torr. After the baking, the efficiency of LED improved as much as 5 times.
The Al mole fraction and doping concentration of each layer in the fabricated LED structure were optimized by simulation.
The data is as follows: Al mole fractions were 0.48, 0.36, and 0.7 and doping concentrations were $5\times10^{17}cm^{-3}$, $2\times10^{16}cm^{-3}$, and $2\times10^{17}cm^{-3}$ in the n-cladding layer, active layer, and p-cladding layer, respectively.
Electro-luminescence and photo-luminescence spectrum were measured on the fabricated samples. It can be seen from the data that there were many impurity levels in the forbidden band gap and therefore optical output power was much degraded. The optical output power was 100$\mu$W at the injection current of 20mA.
