Suppressing the incorporation of carbon impurity in AlGaN:Mg for green LDs with low operation voltage (Conference Presentation)

Abstract

This paper reports the influence of carbon impurities on electrical properties of AlGaN: Mg layer which is used in InGaN-based blue/green laser diodes (LDs) as the cladding layer. AlGaN layer grown by MOCVD usually contains more carbon impurity than GaN, especially when AlGaN is grown at a low temperature to avoid the degradation of InGaN/GaN quantum wells in green LD with high indium content. However, no experimental study on the effect of carbon impurity on the electrical properties of the AlGaN:Mg layer has been reported. All AlGaN:Mg samples were grown on c-plane GaN/sapphire template at various growth pressure, growth rate and V/III ratio to suppress the carbon impurity concentration. These sample were then activated at 950℃ for 90s in nitrogen ambient. The hole concentration and resistivity of Al0.07Ga0.93N:Mg samples depend on carbon concentration. By reducing carbon concentration from 2×1018 to 5×1016 cm-3, the hole concentration increase from 7.5×1016 to 3.5×1017 cm-3, and thus the resistivity of p-Al0.07Ga0.93N decreases from 7.4 to 2.2 Ω·cm . Based on the analysis of the charge neutrality equation, we believe that the compensation effect of CGa(Al) as a shallow donor in AlGaN:Mg explains the dependence of the hole concentration and the resisitivity on the carbon concentration in our samples, which will be discussed in detail in this report. By applying the optimized AlGaN:Mg grown at low temperature as the cladding layer, we have obtained green LD structures without thermal degradation in the InGaN active region. The differential resistance is 2.4 Ω leading to V= 4.9 V at 4 kA/cm2. It lases at 508nm with Jth= 1.8 kA/cm2, and has a output power of 58 mW at a current density of 6 kA/cm2.