Surface band-bending effects on the optical properties of indium gallium nitride multiple quantum wells

Abstract

We report the use of selective wavelength excitation to examine the surface band-bending effects on the optical properties of 3.0-nm-thick indium gallium nitride ͑InGaN͒ multiple quantum wells ͑MQWs͒. Under a 355-nm excitation, the In 0.18 Ga 0.82 N well emission exhibits a linear dependence on the injected carrier density (N inj ) with a coefficient of ͑i͒ 8.5ϫ10 Ϫ18 meV cm 3 for the spectral blueshift and ͑ii͒ 3ϫ10 Ϫ14 V cm 2 for the change of internal field at a density up to N inj ϳ10 19 cm Ϫ3 at 77 K. When excited by a shorter wavelength at 248 nm, the emission from the thin GaN cap layer quenches, but that from the InGaN wells prevails. These observations are attributed to the transportation of photogenerated carriers from the bent GaN surface and redistribution in the InGaN wells. By solving the rate and Poisson equations with a Fermi-level pinning in the band-structure analysis, the emission from the InGaN/GaN MQWs is shown dominant by the recombination between the high-lying subbands and the screening of internal field effects.From recent developments in the material growth and device processing on aluminum indium gallium nitride ͑Al-InGaN͒, this material system has emerged as a promising light source spanning a wide spectral range from ultraviolet to red. 1 Commercialization of candela-class InGaN quantumwell ͑QW͒ blue/green light-emitting diodes, 2 and longlifetime violet and blue laser diodes 3 are examples of such exciting achievements. Despite the progress that has been made in active layer design, 4 many of its peculiar optical properties still remain a great mystery to be solved. 5 A prevailing theory ascribes the emission mechanism to the localized states 6 from the growth of InGaN layer. 7 Alternatively, a characteristic internal field distribution, arisen from the discontinuity of piezoelectricity ( P pz ) and spontaneous polarization ( P sp ) at the nitride interface, 8 can also respond to the change of oscillator strength in spectral analysis. 9 A general assumption is that the recombination is governed by the localized states at low temperature, whereas at high temperature, it is controlled by the extended states. A recent study, 10 however, reveals a drastic reduction in the stability of localized exciton due to the large internal field 11 and carrier screening effects 12 in the InGaN/GaN QW. This makes the treatment of field distribution inside the nitride multiple QWs ͑MQWs͒ an important consideration for the optical analysis. 13 The discontinuity of P sp and P pz at the cap/air interface also imposes a disturbance on the boundary condition. The resultant surface charge, which can be as large as 2ϫ10 13 cm Ϫ2 , constitutes another issue to be resolved in the band-structure analysis. 14 In this letter, we report a series of photoluminescence ͑PL͒ experiments by selective wavelength excitation at vari-ous temperatures to examine the surface band-bending effects on the optical properties of InGaN/GaN MQWs. We find it essential to include a Fermi-level pinning in the GaN cap layer 15 to quant...

Strain relaxation in InxGa1‐xN/GaN quantum well structures

“…From Eq. (3), the value of the piezoelectric field in the quantum well was found to be around 3 MV/cm, which is in agreement with the previously reported values with 20% InN [10]. The same value for the electric field is deduced from the experimental points shown in region I.…”

“…3 can be also divided into three regions. In region I, no relaxation has occurred as L R for the relaxation of In 0.2 Ga 0.8 N on unstrained GaN is 34 Å, in agreement with [10].…”

Faceted sidewall etching of n-GaN on sapphire by photoelectrochemical wet processing

“…The surface after PEC treatment results in a raised surface (i.e., the exposed surface after PEC treatment is above, rather than below, the masked surface) as shown in the oblique-incidence SEM shown in Fig. 20 For c-plane orientations, these effects result in large internal electric fields, and thus enhance the photooxidation process, whereas along the nonpolar m-plane directions in GaN such field action is minimized. As can be seen, this raised surface exhibits significant cracking, but the cracks are confined to the regions of the surface that were exposed to the PEC treatment; they do not propagate into the areas that were masked with Ti during the treatment.…”

Calculation of electric field and optical transitions in InGaN∕GaN quantum wells

“…98, 073522 ͑2005͒ ergies and/or internal field. Peng et al 35 use selective wavelength excitation with photoluminescence, Wang et al 15 photoluminescence under high excitation, Lai et al 6 electrotransmission, Dhar et al 14 Where internal field is reported in the experimental work, the field is deduced from E tr ͑as a function of applied bias in the case of Takeuchi et al, 4 Lai et al, 6 and Jho et al, 7 and as a function of well width in the case of Hangleiter et al 34 ͒. Our internal fields and blueshifts tend to be on the high side ͑although the match with another theory paper ͑Xiao and Kim 17 ͒ is reasonably good͒.…”