Luminescence spectra and efficiency of GaN-based quantum-well heterostructure light emitting diodes: Current and voltage dependence

Luminescence spectra and quantum yield in light emitting diodes (LEDs) base d on InGaN/AlGaN/GaN heterostructures with multiple quantum wells (MQWs) we re studied in the range of currents J = 10(-6)-10(-1) A. Minor spread in th e quantum yield at operating currents (+/- 15% at J approximate to 10 mA) w as observed in these LEDs, which were fabricated by Hewlett-Packard. The sp read is due to differences in the current and voltage dependences of the di ode emission intensity, caused by differences in the charged center distrib ution across the space-charge region (SCR) of the structures and in the rol e of the tunnel current component at low voltages. In the diodes with a thi n (less than or similar to 120 nm) SCR, a tunnel emission band was observed for J less than or similar to 100 muA; the peak energy of this band (h) ov er bar omega (max) = 1.92-2.05 eV corresponds to the voltage applied. At lo w currents (J = 0.05-0.5 mA), the spectral position of the main peak (h) ov er bar omega (max) = 2.35-2.36 eV is independent of the voltage and is dete rmined by the radiative transitions between the localized states. At J > 1 mA, this band shifts with the current (h omega (max) = 2.36-2.52 eV). Its s hape corresponds to the model for the occupation of states in the two-dimen sional energy band tails, which are caused by the microscopic potential flu ctuations. The four parameters in this model are related to the calculated energy band diagram of the MQW structure. (C) 2001 MAIK "Nauka /Interperiod ica".