Electrical Properties and Luminescence Spectra of Light-Emitting Diodes with Modulated Doped InGaN/GaN Quantum Wells
- PDF / 222,321 Bytes
- 5 Pages / 595 x 842 pts (A4) Page_size
- 18 Downloads / 244 Views
Electrical Properties and Luminescence Spectra of Light-Emitting Diodes with Modulated Doped InGaN/GaN Quantum Wells A.E.Yunovich, S.S.Mamakin M.V.Lomonosov Moscow State University, Dept. of Physics, 119899 Moscow, RUSSIA F.I.Manyakhin, A.B.Wattana Moscow Inst. of Steel and Alloys, 119899 Moscow, RUSSIA N.Gardner, W.Goetz, M.Misra, S.Stockman LumiLeds Lighting, San Jose, CA, USA ABSTRACT
Charge distributions N(z) and electroluminescence spectra of blue and green light-emitting diodes (LEDs) based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells. MQWs were modulated doped by Si donors in GaN barriers, electrons from donors being in InGaN wells. N(z) were determined using dynamical capacitance (C-V) method. Acceptor and donor concentrations near the p-n- junction were approximately NA ≥1.1019 cm-3 >> ND ≥ 1.1018 cm-3. Functions N(z) have periodic maxima and minima; their number was 4 and a period of 10 ÷15 nm, according to the details of growth. The extrema reflect charge distributions in MQWs on the n-side of the junctions with accuracy in z of the order of the Debye length (2-3 nm). An energy diagram of the structures is calculated according these measurements. Shifts of spectral maxima with current (J = 10-6 – 3.10-2 A) for these LEDs are comparatively low (3-12 meV for blue LEDs and 20-50 meV for green ones), much less than for previously studied green LEDs (up to 150 meV). This behavior is explained by screening of piezoelectric fields by electrons in the wells. Quantum efficiency versus current is correlated with N(z) distributions and currentvoltage characteristics of the LEDs. INTRODUCTION Mechanisms of radiative recombination in InGaN/AlGaN/GaN p-n- heterostructures with MQWs depend on high electric fields in the structures caused as by p-n- doping on both sides of the heterojunctions, as also by piezoelectric and spontaneous polarization in MQWs [1-3]. The polarization electric field in InGaN wells is directed in the opposite direction to the electric field of the p-n- junction if the structures are grown on a Ga- polar surface. This field divides electrons and holes in the wells if the width of the wells is comparable or greater than exciton radius and is the cause of quantum-confinement Stark effect [4-5]. The polarization field in GaN and AlGaN barriers is directed in the same direction as the field of the p-n- junction thus making the electric field in the structures of the order of 106 V/cm. High field in GaN- based structures is the cause of tunnel effects [6]. If the barriers in MQWs are doped by donors, electrons from the donors fall down to the wells. Electrons are screening surface charges on heterointerfaces and the electric field in the structures may be sufficiently lower than in undoped structures. The probability of radiative recombination in the wells is enhanced if the quantum-confinement Stark effect is depressed and a role of tunnel effects is lowered in lower electric fields. Thus the efficiency of LEDs based on these structures is higher than in undoped structures as was
Data Loading...
