Effective band gap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures

Abstract

The emission mechanisms of strained In x Ga 1Ϫx N quantum wells ͑QWs͒ were shown to vary depending on the well thickness, L, and x. The absorption edge was modulated by the quantum confined Stark effect and quantum confined Franz-Keldysh effect ͑QCFK͒ for the wells, in which, for the first approximation, the product of the piezoelectric field, F PZ , and L exceed the valence band discontinuity, ⌬E V. In this case, holes are confined in the triangular potential well formed at one side of the well producing the apparent Stokes-like shift. Under the condition that F PZ ϫL exceeds the conduction band discontinuity ⌬E C , the electron-hole pair is confined at opposite sides of the well. The QCFK further modulated the emission energy for the wells with L greater than the three dimensional free exciton Bohr radius a B. On the other hand, effective in-plane localization of carriers in quantum disk size potential minima, which are produced by nonrandom alloy compositional fluctuation enhanced by the large bowing parameter and F PZ , produces a confined electron-hole pair whose wave functions are still overlapped ͑quantized excitons͒ provided that L Ͻa B .

Physics of high-power InGaN/GaN lasers

“…This is mainly attributed to charged defects at hetero interfaces which partially screen the polarisation field. The actual polarisation field in our quantum wells is unknown and we assume 20% of the calculated polarisation charges corresponding to a 340 kV=cm QW polarisation field, which is close to experimental results on similar quantum wells [27]. This assumption doubles the calculated threshold current due to quantum well gain reduction by the separation of electron and hole wave functions (Fig.…”

Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells

“…Established reasons for this matter include a reduced electron-hole-overlap in the QWs due to the quantumconfined Stark effect (QCSE) [4][5][6][7][8] and general difficulties in growing homogeneous InGaN material. [9][10][11][12][13][14][15] Also high pumping conditions are known to cause a further reduction of the efficiency that is attributed to Auger recombination. [16][17][18][19] In this letter, we report on an additional high excitation loss mechanism arising from confined hole continuum (CHC) states promoting carrier leakage, which is of utmost importance for the implementation of efficient LDs emitting in the green spectral region.…”

Ultrafast carrier relaxation in GaN,In0.05Ga0.95N,and anÖzgür1, Everitt2 2003Phys. Rev. B

“…5 Such inhomogeneities have been observed for InGaN MQWs having even less than 15 % In. 7,35 Carrier localization due to inhomogeneities is also expected to decrease with Si doping in the barriers. 34 As the size of In-rich regions grow, the confinement within large dots is reduced and the Stokes' shift increases.…”