Improvement of InGaN/GaN laser diodes by using a Si-doped In/0.23/Ga/0.77/N/GaN short-period superlattice tunneling contact layer

InGaN/GaN multiple-quantum-well laser diode (LD) structures, including an Si-doped n/ /-In/0.23/Ga/0.77/N/GaN short-period superlattice (SPS) tunneling contact layer, are grown on c-face sapphire substrates by metalorganic vapor-phase epitaxy. The In/0.23/Ga/0.77/N/GaN(n/ /)-GaN(p) tunneling junction, which uses a low-resistivity n/ /-In/0.23/Ga/0.77/N/GaN SPS instead of a 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 LDs with n/ /-In/0.23/Ga/0.77/N/GaN SPS contacting layers can achieve a lower threshold current and longer lasing duration under pulsed operation. Moreover, when the input pulse width is lengthened from 300 ns to 2 mus, the lasing duration of the LD with Pt ohmic contact is three times longer than that of the LD with Ni/Au ohmic contacts. Therefore, we conclude that nitride-based LDs with an SPS reversed-tunneling contact layer may significantly reduce the contact resistance of an anode electrode and thereby increase the thermal stability of the device reliability.