Integration of Emission-Wavelength-Controlled InAs Quantum Dots for Ultra-Broadband Near-Infrared Light Source

Abstract

Near-infrared (NIR) light sources are widely utilized in biological and medical imaging systems owing to their long penetration depth in living tissues. In a recently developed biomedical non-invasive cross-sectional imaging system, called optical coherence tomography (OCT), a broadband spectrum is also required, because OCT is based on low coherence interferometry. To meet these operational requirements, we have developed a NIR broadband light source by integrating self-assembled InAs quantum dots (QDs) grown on a GaAs substrate (InAs/GaAs QDs) with different emission wavelengths. In this review, we introduce the developed light sources and QD growth techniques that are used to control the emission wavelength for broadband emission spectra with center wavelengths of 1.05 and 1.3 μm. Although the strain-induced Stranski-Krastanov (S-K) mode-grown InAs/GaAs QDs normally emit light at a wavelength of around 1.2 μm, the central emission wavelength can be controlled to be between 0.9-1.4 μm by the use of an In-flush technique, the insertion of a strain-reducing layer (SRL) and bi-layer QD growth techniques. These techniques are useful for applying InAs/GaAs QDs as NIR broadband light sources and are especially suitable for our proposed spectral-shape-controllable broadband NIR light source. The potential of this light source for improving the performance of OCT systems is discussed.

Photoelectric properties of the metamorphic InAs/InGaAs quantum dot structure at room temperature

“…It can be noticed that the PL intensity of metamorphic QDs is about just half of the intensity of InAs/ GaAs QDs both at 10 K and RT: this allows to conclude that metamorphic QDs retain a good PL efficiency, 4,12 considering that InAs/GaAs QDs are known to be very efficient light sources. 20,21 The current-voltage characteristics were measured with and without illumination at the peak of photocurrent spectrum ( Figure 3). The photocurrent (inset of Figure 3) is found to rise monotonously when the reverse bias is increased, with a weaker rise at greater bias values.…”

“…4,12,18 The emission efficiency was confirmed also for the structure investigated in this work on the basis of a comparison with PL intensities of structures with InAs QDs grown on GaAs, known to be very efficient light sources. 20,21 It should be mentioned here that, thanks to the possibility of changing the QD emission by acting on MB parameters such as composition and thickness, metamorphic QD nanostructures can allow to tune the QD emission in the windows of optoelectronic interest at 1.3 and 1.55 lm. 3,4 Photoelectric and absorption spectroscopy allows to investigate more transitions in comparison with PL characterization, as shown in Figure 4(a).…”

Imaging of spectral-domain optical coherence tomography using a superluminescent diode based on InAs quantum dots emitting broadband spectrum with Gaussian-like shape

“…The emission wavelength of each QD was controlled by varying the thickness of the strain-reducing layer (SRL) 21,22) deposited on each QD: 0, 1.0, 1.9, and 4.0 nm. Although the growth parameters were almost identical to those of the previous reported sample, 19,23) the variation in the SRL thickness and the growth conditions of the QD were optimized in order to obtain emissions with a Gaussian-like spectral shape from the QDs. A straight ridge waveguide (RWG) with the height of 1.4 µm and the width of 25 µm was fabricated on the grown wafer.…”

Optical characterization of In-flushed InAs/GaAs quantum dots emitting a broadband spectrum with multiple peaks at ~1 μm

“…Recently, a broadband light source based on InAs QDs was developed and achieved a bandwidth of over 200 nm [ 9 – 12 ]. However, the InAs/GaAs QDs typically emit light of approximately 1.2–1.3 μm wavelength; therefore, we have developed various methods to control the emission wavelength of InAs QDs [ 13 ]. For the adjustment of the emission wavelength to the 1 μm regime, we have utilized the In-flush technique [ 14 , 15 ].…”