Time Evolution of the Screening of Piezoelectric Fields in InGaN Quantum Wells

• Published in: IEEE journal of quantum electronics 2006-12, Vol.42 (12), p.1202-1208
• Main Authors: Brown, I.H., Blood, P., Smowton, P.M., Thomson, J.D., Olaizola, S.M., Fox, A.M., Parbrook, P.J., Chow, W.W.
• Format: Article
• Language: English
• Subjects: Carrier density; Charge carrier density; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Emission; Evolution; Exact sciences and technology; Excitation; Fundamental areas of phenomenology (including applications); Gallium nitride; Iii-v semiconductors; Indium gallium nitrides; Laser materials; Lasers; Optical materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical pulses; Optics; Photoluminescence; Photonic band gap; Physics; Piezoelectricity; Piezoelectricity and electromechanical effects; Pulse measurements; Radiative recombination; Screening; Semiconductor lasers; laser diodes; Space vector pulse width modulation; Stimulated emission; Time factors; Time measurement; Wells
• ISSN: 0018-9197; 1558-1713
• DOI: 10.1109/JQE.2006.883472

We have measured the time response of the emission spectra of In 0.07 Ga 0.93 N quantum wells with widths of 2, 3, and 4nm in GaN following pulsed optical excitation. We observe a blue shift of the emission peak during the excitation and a subsequent red shift as the carriers recombine in the 3- and 4-nm wells, and a negligible shift for the 2-nm well. Using a comprehensive theory we are able to fit both the time evolution of the peak emission energy and the integrated emission intensity. The shift of the emission peak (by about 17 meV) arises from the balancing of the change in screening of the internal piezoelectric field as the carrier density changes and bandgap renormalization. We have projected the calculations to quantify the degree of screening at typical threshold carrier densities. At transparency we estimate carrier densities of 4.3times10 16 m -2 and 4.8times10 16 m -2 for the 4- and 3-nm wells, respectively, which reduce the internal piezoelectric field in the well to 0.97times10 8 (4 nm) and 1.03times10 8 (3 nm) Vmiddotm -1 compared with the unscreened value of about 1.23times10 8 Vmiddotm -1 . Thus, a substantial field remains in these wells under laser conditions. We find that this partially screened field is beneficial in reducing the threshold current compared with that of a square well for modal gains up to about 150 cm - 1