The Emission Properties of Light Emitting Diodes using InGaN/AlGaN/GaN Multiple Quantum Wells

1998 
Luminescence spectra of Light Emitting Diodes (LEDs) with Multiple Quantum Wells (MQWs) were studied at currents J = 0.15 μA - 150 mA. A high quantum efficiency at low J is caused by a low probability of the tunnel current J (which is maximum at J m ≈ 0.5-1.0 mA). J(V) curves were measured in the range J= 10 −12- 10 −1 A; at J > 10 −3 A they may be approximated by a sum of four parts: V= φ k + mkT·[ln(J/J 0 )+(J/J 1 ) 0.5 ] + J·R s . The part V ~ (J/J 1 ) 0.5 is the evidence of a double-injection into i-layers near MQWs. Their presence is confirmed by capacitance measurements. An overflow of carriers through the MQW causes a lower quantum efficiency at high J. A model of a 2D-density of states with exponential tails fits the spectra. The value of T in the active layer was estimated. A new band was detected at high J; it can be caused by non-uniformity of In content in MQWs.
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