Piezoelectric Field and its Influence on the Pressure Behavior of the Light Emission from InGaN/GaN and GaN/AlGaN Quantu
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Piezoelectric Field and its Influence on the Pressure Behavior of the Light Emission from InGaN/GaN and GaN/AlGaN Quantum Wells T. Suski 1, P. Perlin 1, S.P. Lepkowski 1, H. Teisseyre 1, I. Gorczyca1, P. Prystawko 1, M. Leszczynski 1, N. Grandjean 2, and J. Massies 2, T. Kitamura 3, Y. Ishida 3, S.F. Chichibu 3, *
, and H. Okumura 3,
1
High Pressure Research Center, “Unipress”, 01-142 Warsaw, Poland
2
CRHEA - Centre National de la Recherche Scientifique, 06560 Valbonne, France
3
Power Electronics Research Center 2, National Institute of Advance Industrial Science and
Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
ABSTRACT
In this paper we review studies aiming at elucidation of the mechanisms responsible for anomalously low pressure coefficients of the light emission energy, dEE/dP, observed in quantum structures of InGaN/GaN and GaN/AlGaN. We have established that in hexagonal InGaN/GaN and GaN/AlGaN structures the main mechanism involved is related to the pressure induced increase of the piezoelectric field which determines also the strong red shift of the emission energy with thickness of the quantum well. To reproduce the experimental findings in InGaN/GaN case, it is necessary to take into account the dependence of the piezoelectric constants on the volumeconserving strain. Whereas the experimental results on a decrease of dEE/dP in GaN/AlGaN structures can be fully accounted for within the linear elasticity theory. In contrast to these findings, dEE/dP magnitude measured in cubic InGaN/GaN quantum structures shows value close to changes of the InGaN bangap with pressure obtained from first principle calculations. The latter result is consistent with the absence of the built-in electric fields in the cubic nitride structures.
INTRODUCTION
Contribution of the built-in electric field to the properties of wurtzite group-III nitrides has been widely disputed during last few years [1-3]. The considered materials exhibit a pyroelectric properties and strong piezoelectric character which lead to the appearance of the electric I7.6.1
polarization due interface charge accumulation. It consists of two contributions: i) piezoelectric polarization due to strain induced by a lattice-mismatch [4,5] and ii) the spontaneous polarization. The latter effect is present even in the bulk - unstrained nitrides and originates from a relative shift of the cation and anion sublattices along c axis of the wurtzite polar structure [1]. Effects resulting from the built-in macroscopic polarization can entirely determine some basic properties of nitrides. In case of nitride systems consisting of the layers crystallizing in the cubic structure neither spontaneous nor piezoelectric polarizations are present in one of the equivalent directions. In wurtzite nitride structures the effective electric field, directed along c axis (epitaxial growth direction) caused by i) and ii) leads to a bending of the potential profiles related to the conduction and valence bands in quantum structures consisting of I
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