Optical Gain Spectra of a (0001) InGaN Green Laser Diode

Funato, Mitsuru; Kim, Yoon Seok; Ochi, Yoshiaki; Kaneta, Akio; Kawakami, Yoichi; Mutoh, T.; Nagahama, Shin–ichi

doi:10.7567/apex.6.122704

Cited by 19 publications

(13 citation statements)

References 23 publications

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“…In addition to the homogeneous broadening, frequently used in ZB QWs [24,63], parametrized here by sech with 10 meV full width at half-maximum (FWHM), we also consider an inhomogeneous Gaussian broadening, attributed to compositional and potential fluctuations. Our choice of Gaussian broadening with 20 meV FWHM is consistent with a decreased broadening for smaller emission wavelengths in (In,Ga)N QW lasers and reported values relevant for wavelengths of ∼415 nm [64] which corresponds to the typical energy of the gain peak in our calculations. Because of the broadening effects, the individual CB1-HH1 and CB1-LH1 transitions that dominate the gain spectra cannot be distinguished [HH1 and LH1 are 10 meV apart, see Fig.…”

Section: Microscopic Spin-dependent Gainsupporting

confidence: 85%

Wurtzite spin lasers

Faria

Chen

et al. 2017

Phys. Rev. B

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Semiconductor lasers are strongly altered by adding spin-polarized carriers. Such spin lasers could overcome many limitations of their conventional (spin-unpolarized) counterparts. While the vast majority of experiments in spin lasers employed zinc-blende semiconductors, the room temperature electrical manipulation was first emonstrated in wurtzite GaN-based lasers. However, the underlying theoretical description of wurtzite spin lasers is still missing. To address this situation, focusing on (In,Ga)N-based wurtzite quantum wells, we develop a theoretical framework in which the calculated microscopic spin-dependent gain is combined with a simple rate equation model. A small spin-orbit coupling in these wurtzites supports simultaneous spin polarizations of electrons and holes, providing unexplored opportunities to control spin lasers. For example, the gain asymmetry, as one of the key figures of merit related to spin amplification, can change the sign by simply increasing the carrier density. The lasing threshold reduction has a nonmonotonic depenedence on electron spin polarization, even for a nonvanishing hole spin polarization.

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Section: Microscopic Spin-dependent Gainsupporting

confidence: 85%

Wurtzite spin lasers

Faria

Chen

et al. 2017

Phys. Rev. B

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“…The measurement of optical gain is used to show the change in the efficiency and that the wide QWs can be used in real-life devices. The optical gain in InGaN LDs has been widely studied, and it was shown that it suffers from the green gap problem just as LEDs do. − There are two major causes of the decrease of optical gain for long wavelength LDs: (i) “droop” of quantum efficiency and (ii) lower optical confinement factor (Γ). The decrease of Γ is due to a lower refractive index contrast between the alloys as the operating wavelength increases .…”

Section: Optical Gain Of Wide Ingan Qwsmentioning

confidence: 99%

Beyond Quantum Efficiency Limitations Originating from the Piezoelectric Polarization in Light-Emitting Devices

et al. 2019

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Blue and violet light-emitting devices based on III-nitrides caused an ongoing revolution in general lighting. One of the highly deliberated discussions in this field is devoted to the problem called the “green gap”, which is a lack of efficient emitters in this spectral regime. One of the reasons behind the insufficient internal quantum efficiency (IQE) of green III-nitride devices is related to the quantum confined Stark effect. In this paper we present a counterintuitive feature of quantum well systems with a large built-in electric field that leads to a huge enhancement in IQE. We show, by means of numerical simulations, that an increase in the InGaN quantum well thickness initially leads to a decrease in the oscillator strength; however, after a certain critical thickness is reached, a highly efficient recombination path appears via excited states. A peculiar quantum well system with a zero-probability transition between the ground states and an extremely high one through the excited states is demonstrated. Remarkably, the oscillator strength in a wide QW is higher than in conventionally used QWs with thicknesses lower than 5 nm. Experimental evidence is provided showing a change in the nature of the optical transition with increasing thickness of the QW. Furthermore, we show that, counterintuitively, the devices with higher In content exhibit a higher enhancement in IQE, which might solve some problems related to the “green gap”. The predictions shown in this paper are valid for all semiconductor systems exhibiting large piezoelectric polarization such as III-nitrides, II-oxides, and II-sulfides.

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“…39 Note in this respect that the reported inhomogeneous linewidth broadening values of InGaN QWs extracted from gain spectra in state of the art cyan-green wavelength III-nitride LDs indeed exhibit a moderate increase over this wavelength range. 40,41 Finally, let us emphasize that the ability to control the surface morphology and hence the homogeneity of thick InGaN epilayers is extremely relevant in the framework of applications where the minimization of unwanted disorder is critical. This is especially the case when attempts are made to realize laser waveguides, 42 metamorphic layers, 43 or solar cells.…”

Section: -mentioning

confidence: 99%

Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations

Butté

Lahourcade

Uždavinys

et al. 2018

Applied Physics Letters

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To assess the impact of random alloying on the optical properties of the InGaN alloy, high-quality InxGa1−xN (0 < x < 0.18) epilayers grown on c-plane free-standing GaN substrates are characterized both structurally and optically. The thickness (25–100 nm) was adjusted to keep these layers pseudomorphically strained over the whole range of explored indium content as checked by x-ray diffraction measurements. The evolution of the low temperature optical absorption (OA) edge linewidth as a function of absorption energy, and hence the indium content, is analyzed in the framework of the random alloy model. The latter shows that the OA edge linewidth should not markedly increase above an indium content of 4%, varying from 17 meV to 30 meV for 20% indium. The experimental data initially follow the same trend with, however, a deviation from this model for indium contents exceeding only ∼2%. Complementary room temperature near-field photoluminescence measurements carried out using a scanning near-field optical microscope combined with simultaneous surface morphology mappings reveal spatial disorder due to growth meandering. We conclude that for thick high-quality pseudomorphic InGaN layers, a deviation from pure random alloying occurs due to the interplay between indium incorporation and longer range fluctuations induced by the InGaN step-meandering growth mode.

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Optical Gain Spectra of a (0001) InGaN Green Laser Diode

Cited by 19 publications

References 23 publications

Wurtzite spin lasers

Wurtzite spin lasers

Beyond Quantum Efficiency Limitations Originating from the Piezoelectric Polarization in Light-Emitting Devices

Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations

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