The Emission Properties of Light Emitting Diodes using InGaN/AlGaN/GaN Multiple Quantum Wells
- PDF / 232,693 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 201 Views
Internet Journal Nitride Semiconductor Research
The Emission Properties of Light Emitting Diodes using InGaN/AlGaN/GaN Multiple Quantum Wells A. E. Yunovich1, V. E. Kudryashov1, A. N. Turkin1, A. Kovalev2 and F. Manyakhin2 1M.V.Lomonosov 2Moscow
Moscow State University,
Institute of Steel and Alloys,
(Received Sunday, June 21, 1998; accepted Friday, October 23, 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 Jm ≈ 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= ϕk + mkT·[ln(J/J0)+(J/J1)0.5] + J·Rs. The part V ∼ (J/J1)0.5 is the evidence of a doubleinjection 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.
1
Introduction
Recombination mechanisms in InGaN/AlGaN/GaN heterostructures are not fully understood in spite of the great progress in the development of GaN-based lightemitting diodes (LEDs). A model of radiative recombination in 2D-structures with band tails caused by potential fluctuations was successfully applied to luminescence spectra of LEDs with single quantum wells (SQW) [1] [2] [3] [4] [5] and radiative recombination by tunneling was detected at low currents [3] [4] [5] [6] [7] [8]. There is evidence of the fact that phase separation can take place during the growth of InGaN active thin layers (quantum wells). Clusters (quantum dots) with a higher In content may be formed [9]. But no attempts have been reported to describe the spontaneous emission spectra of LEDs using a model of recombination in such clusters. It was interesting to study details of luminescence spectra of working LEDs recently developed with multiple quantum wells (MQW) [10] [11] and to compare their properties with those of LEDs with SQWs. In this work samples of blue and green LEDs with MQW InGaN/GaN active layers [10] [11] were studied
at a wide range of currents. A model of radiative recombination in 2D-structures with band tails is applied to describe the luminescence spectra. Charge and electric field distributions for LEDs with SQWs and MQWs are compared. The mechanisms of recombination in GaNbased MQWs are discussed. 2
Experimental
Blue and green LEDs based on InxGa1-xN/AlyGa1-y/ GaN heterostructures were studied [10] [11]. Structures were grown by MOCVD on sapphire substrates with an AlN buffer layer (30 nm) followed by a base n-GaN: Si layer (4–5 µm). An InxGa1-xN/GaN MQW structure was grown on the base. The number of periods in the MQW varied; samples with 5 periods were chosen for the study; the thic
Data Loading...
