Low-operation voltage of InGaN/GaN light-emitting diodes with Si-doped In_0.3Ga_0.7N/GaN short-period superlattice tunnelling contact layer

InGaN/GaN multiple-quantum-well light-emitting diode (LED) structures including a Si-doped In_0.23Ga_0.77N/GaN short-period superlattice (SPS) tunnelling contact layer were grown by metalorganic vapour phase epitaxy. The In_0.23Ga_0.77N/GaN(n⁺)-GaN(p) tunnelling junction, which the low-resistivity n⁺-In_0.3Ga_0.7N/GaN SPS instead of high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form a "ohmic" contact. In this structure, the sheet electron concentration of Si-doped In_0.23Ga_0.77N/GaN SPS is around 1 × 10¹⁴/cm², leading to an averaged electron concentration of around 1 × 10²⁰/cm³. This high-conductivity SPS would lead to a low-resistivity ohmic contact (Au/Ni/SPS) of LED. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 2.95 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V.