The influences of Al_xGa_1-xN layer on the characteristics of UV LED structure

We have studied growth characteristics of Al_xGa_1-xN/GaN epilayers which were grown with various x values and their effects on the characteristics of UV LED chips fabricated by Al_xGa_1-xN/GaN double heterojunction having different band offset. The van der Pauw technique, double crystal X-ray diffractometry (DCXRD), optical microscope and photoluminescence (PL) were used to characterize crystallographic, electrical and optical properties of each Al_xGa_1-xN epilayer. The device characteristcs of the fabricated UV LED chips were evaluated by measuring current - voltage (I-V) and light power-current (L-I) measurements were carried out. The PL spectra and the DCXRD results show that the dislocation density of Al_xGa_1-xN epilayer resulted from the difference of lattice mismatch between Al_xGa_1-xN and GaN and the FWHM increases by raising the Al incorporation. The turn-on voltage of the UV LED chips fabricated by Al_xGa_1-xN/GaN double heterojunction is less dependent on both the x value of Al_xGa_1-xN cladding layer and the related band offset (ΔE_g). It was found that the optical power is strongly dependent on the dislocation density of each Al_xGa_1-xN cladding layer related to the individual x value.