Improvement of InGaN/GaN laser diodes by using a Si-doped In_0.23Ga_0.77N/GaN short-period superlattice tunneling contact layer

InGaN/GaN multiple-quantum-well laser diode (LD) structures, including a Si-doped n⁺-In_0.23Ga_0.77N/GaN short-period superlattice (SPS) tunneling contact layer, were grown on c-face sapphire substrate by metalorganic vapor-phase epitaxy. The In_0.23Ga_0.77N/GaN(n⁺)-GaN(p) tunneling junction, which used the low-resistivity n⁺-In_0.23Ga_0.77N/GaN SPS instead of the high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form a "quasi-ohmic" contact. Experimental results indicate that the LDs with n⁺-In_0.23Ga_0.77N/GaN SPS contacting layer can achieve a lower threshold current and longer lasing duration under pulsed operation. Moreover, when the input pulse width was lengthened from 300 ns to 2 μs, the lasing duration of the LD with Pt ohmic contact was three times longer than that of the LD with Ni/Au ohmic contact. Therefore, one would like to conclude that nitride-based LDs with an SPS reversed-tunneling contact layer will significantly reduce the contact resistance of an anode electrode and thereby increase the thermal stability of the device reliability.