Discrete Steps in the Capacitance-Voltage Characteristics of GalnN/GaN Light Emitting Diode Structures
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Discrete Steps in the Capacitance-Voltage Characteristics of GaInN/GaN Light Emitting Diode Structures Y. Xia1,2, E. Williams1,2, Y. Park2,3, I. Yilmaz1,2, J.M. Shah2,3, E.F. Schubert1,2,3, C. Wetzel1,2 1 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 2 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 3 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A.
ABSTRACT A detailed modeling of the electronic bandstructure of GaInN alloys and GaInN/GaN heterostructures typically used for high efficiency light emitting diodes is of high relevance for future improvements. Here we are exploring opportunities to accurately quantify the carrier dynamics under forward and reverse voltage bias. In GaInN/GaN LED-type heterostructures we observe distinct steps in the junction capacitance as a function of bias voltage within the depletion regime. Up to three individual steps can be identified that correspond to alternating ranges of capacitive and resistive impedances. Our analysis suggests that we are quantitatively monitoring the electron concentration in each individual quantum well. The pronounced clarity of the data reveals a high level of epitaxial perfection and spatial homogeneity across the entire area of the junction.
INTRODUCTION III-nitride Quantum Well (QW) structure semiconductors have attracted much interest in recent years because they are known as promising materials for green, blue, and UV light emitting diodes (LED) [1-2]. It is known that huge piezoelectric fields exist in GaN-based heterostructures with wurtzite crystal structure [3-5]. In GaInN layers biaxially compressed to GaN in typical Ga-face growth along the c-axis, the piezoelectric field is opposite to the growth direction [3, 4]. As a result the electron and hole wavefunctions in the QW are subjected to the quantum confined Stark effect (QCSE) even without an external electric field. When we apply an additional reverse bias voltage, the transition energy shows a blue-shift since piezoelectric field is compensated [3]. Thus the application of an external electric field perpendicular to the layers of QWs significantly changes the photoluminescence (PL) properties [6, 7]. On the other hand, capacitance-voltage (C-V) measurements are widely used to determine the carrier concentration in a p-n diode. Here we combine both methods in an attempt to quantify the net charges present at the individual heterointerfaces and to analyze the carrier depletion dynamics. This report presents C-V measurements of the GaInN/GaN QWs embedded in the depletion region of a specially designed p+-n junction LED. We correlate this data with both PL and photocurrent (PC) data as a function of the bias voltage from deep depletion up to forward injection.
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EXPERIMENTAL For the experiments, we used GaInN/GaN multiple quantum well (MQW) structure consisting of five wells embedded in a p-n diode. The acc
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