A Role of the Built-in Piezoelectric Field in InGaN/AlGaN/GaN Multiple Quantum Wells in the Electroferlectance Experimen
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1040-Q07-10
A Role of the Built-in Piezoelectric Field in InGaN/AlGaN/GaN Multiple Quantum Wells in the Electroferlectance Experiments Pavel Bokov1, Lev Avakyants1, Mansur Badgutdinov1, Anatoly Chervyakov1, Stanislav Shirokov1, Alexander Yunovich1, Elena Vasileva2, Feodor Snegov2, Dmitry Bauman2, and Boris Yavich2 1 Physics faculty, M.V. Lomonosov Moscow State University, Leninskie gory 1 building 2, Moscow, 119992, Russian Federation 2 2JSC “Svetlana-Optoelectronica”, Saint-Petersburg, Russian Federation ABSTRACT The influence of built-in piezoelectric field in the light-emitting diodes based on InGaN/AlGaN/GaN heterostructures on the electroreflectance spectra have been studied. The structures were grown by MOCVD technology and «flip-chip» mounted. Light was emitted or reflected through sapphire substrate. The interference fringes and spectral line connected with the InGaN/GaN multiple quantum wells region are observed in the electroreflectance spectra. Observed blue shift of spectral line from InGaN/GaN multiple quantum wells region with the increasing reverse bias voltage has been explained as the result of decreasing of the electric field in the quantum well. INTRODUCTION It is possible to observe reflectance and electroreflectance (ER) spectra from InGaN/AlGaN/GaN heterostructure if it is flip-chip mounted by the p- side to the heat sink [1]. In this case the light is focused on the structure through a sapphire substrate and n- layer. The electric field in the structure grown for light-emitting diode (LED) is modulated by applying reverse voltage to the LEDs contacts. There are piezoelectric fields in the heterostructures InGaN/GaN, grown at the (0001) direction, due to the wurtzite nature of GaN compounds. These fields play an important role for the properties of the nitride based LEDs, affecting on the emission wavelength, oscillator strength and recombination lifetime [2]. On the other hand, experimental [3] and theoretical [4] studies show that luminescence and absorption spectra depends on the strain in wurtzite InGaN/GaN heterostructures. Preliminary results of our ER experiments of InGaN/AlGaN/GaN LEDs have shown the influence of the built-in piezoelectric fields on the ER spectra [5 – 6]. In this paper we discuss the results of our ER experiments with the different bias voltages (from +1 to -6 V) on LEDs pnjunction. EXPERIMENT InGaN/AlGaN/GaN p-n- heterostructures for blue LEDs were grown by MOCVD technology on sapphire substrates and flip-chip mounted by p- side to the heat sink. Fig. 1 shows the structure of the samples: the buffer i-GaN layer had the width < 0.5 µm; n-GaN layer - 3.5 µm; 5 quantum wells/barriers InGaN/GaN (active MQW region) - ≅0.003/0.012 µm; electron
blocking layer i-GaN (or p-AlGaN) of ≅0.02 µm and a capping p-GaN layer of ≅0.11 µm. The concentration x of indium in the InxGa1-xN layers was 0.12-0.13. A reflective mirror was made on the p-side of the LED. The area of the chip was ≅0.4 mm2. Some experiments were carried out on the LumiLeds «Luxeon» LEDs. The ER spectra were regi
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