Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

Schwarz, Uli; Lauterbach, C.; Schillgalies, Marc; Rumbolz, C.; Furitsch, M.; Lell, A.; Härle, V.

doi:10.1117/12.662019

Cited by 11 publications

(8 citation statements)

References 26 publications

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“…Thus, our findings might be attributed to a depletion of the surface layers by photon enhanced oxidation, similar to what was observed in the literature [24,25]. Indeed, the area where a significant change in the surface potential is measured (see figure 2) very much resembles the typical near field of an edge emitting device [22,26,27].…”

Section: Resultssupporting

confidence: 89%

Microscopic investigation of InGaN/GaN heterostructure laser diode degradation using Kelvin probe force microscopy

Lochthofen¹,

Mertin²,

Bacher³

et al. 2008

J. Phys. D: Appl. Phys.

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We report on Kelvin probe force microscopy (KPFM) measurements on fresh and artificially aged InGaN/GaN laser test structures. In the case of an unbiased laser diode, a comparison of the surface potential between a fresh and a stressed laser diode shows a pronounced modification of the laser facet due to the aging process. Performing KPFM measurements under forward bias, a correlation between the macroscopic I–V characteristics and the microscopic voltage drop across the heterostructure layer sequence is found. This clearly demonstrates the potential of KPFM for investigating InGaN/GaN laser diode degradation.

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Section: Resultssupporting

confidence: 89%

Microscopic investigation of InGaN/GaN heterostructure laser diode degradation using Kelvin probe force microscopy

Lochthofen¹,

Mertin²,

Bacher³

et al. 2008

J. Phys. D: Appl. Phys.

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“…To prevent heating, the LD was operated in a pulsed mode at a low duty cycle of about 1:1000. Details on this experimental setup can be found in [5].…”

mentioning

confidence: 99%

“…The LD is driven with typically 500 ns long electric pulses and the intensity at each spot of the LD facet picked up with the SNOM fiber is measured with a fast photomultiplier and a sampling oscilloscope. In this way we can measure the near-field and far-field dynamics of the waveguide mode during pulsed operation [2][3][4]. To prevent heating, the LD was operated in a pulsed mode at a low duty cycle of about 1:1000.…”

mentioning

confidence: 99%

Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes

Braun

Lauterbach

Schwarz

et al. 2007

Phys. Status Solidi (c)

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In semiconductor laser diodes, high refractive index epitaxial layers can act as parasitic waveguides and cause severe losses to the mode propagating in the laser waveguide. For (Al,In)GaN laser diodes the parasitic modes are typically caused by the SiC or GaN substrate or buffer layers. Substrate modes have an impact on near-field and far-field of the waveguide mode, on laser threshold, and on gain spectra. We present scanning near-field measurements of the substrate mode and demonstrate that the period of the standing wave in the GaN substrate varies over a wide range and critically depends on the effective refractive index of the waveguide mode.1 Introduction For (Al,In)GaN laser diodes (LD) on bulk GaN substrates the refractive index of the substrate is higher than that of the effective refractive index of the waveguide. Thus any part of the waveguide mode tunneling as evanescent wave through the n-side AlGaN cladding can propagate in the substrate. Reflected under a small angle of incidence from the bottom surface of the substrate it will form a standing wave. This so-called substrate mode causes a periodic modulation of the total loss of the laser mode. We observe this as periodic modulation in the gain spectra measured by the Hakki-Paoli method and by a dependency of the threshold current on the n-cladding layer thickness [1]. The far-field shows side-lobes rising from the substrate mode travelling at an angle to the waveguide which is determined by the effective refractive index of the mode and the refractive index of the substrate. We also observe the standing wave in the substrate by a measurement of the near-field intensity on the cleaved surface of the substrate just below the laser ridge waveguide. This is the most direct observation of the substrate mode.For a quantitative analysis we establish a two-dimensional finite element electromagnetic solver, to simulate periodic variations in the cavity loss that reproduce measurements of the modal gain in terms of absolute value and oscillations amplitude. Details and results of these simulations can be found in [1]. The two-dimensional simulation model shows a periodic interference pattern in the substrate [1], very similar to what can be found in measurements (see Fig. 1). An oscillation period of about 1 µm can be extracted from this pattern. These simulations can be used to optimize the vertical structure (within the constraints given by growth conditions) in order to minimize the impact of the substrate modes [1].Here we concentrate on near-field measurements of the substrate mode intensity distribution. We demonstrate that the spatial period of the substrate mode varies over a wide range and critically depends on the effective refractive index of the waveguide.

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“…1 Introduction One way to measure the near-field intensity distribution of the waveguide modes of a laser diode (LD) is a scanning near-field optical microscope (SNOM), with the fiber tip scanning over the surface of the laser facet ( [1] and others). This method allows to retrieve intensity and spectra with a high spatial resolution of about 50-100 nm.…”

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confidence: 99%

Multidimensional near‐ and far‐field measurements of broad ridge (Al,In)GaN laser diodes

Rogowsky

Braun

Schwarz

et al. 2009

Phys. Status Solidi (c)

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Broad (Al,In)GaN laser diodes (LD) with ridge widths of some micrometers show up multi mode patterns. We analyze (Al,In)GaN LDs with different ridge widths in the UV and blue spectral regime simultaneously with temporal, spectral and spatial resolution in the near‐ and far‐field. We transform the laser beam of the LD by a lens system and get a magnified image of the near‐field. By using a CCD camera we get the near‐field intensity information of the image. In combination of an optical fiber with a photomultiplier or a spectrometer we get the temporal and spectral information. Additionally we can image the propagation from near‐ to far‐field. In this paper we describe the properties of our setup and compare a near‐field (SNOM) and far‐field (imaging with a microscope objective) approach to the measurement of the LDs multi‐dimensional characteristics (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Time-resolved scanning near-field microscopy of InGaN laser diode dynamics

Cited by 11 publications

References 26 publications

Microscopic investigation of InGaN/GaN heterostructure laser diode degradation using Kelvin probe force microscopy

Microscopic investigation of InGaN/GaN heterostructure laser diode degradation using Kelvin probe force microscopy

Experimental and theoretical study of substrate modes in (Al,In)GaN laser diodes

Multidimensional near‐ and far‐field measurements of broad ridge (Al,In)GaN laser diodes

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