Wavelength tunable InAs/InP(1 0 0) quantum dots in 1.55-µm telecom devices

This paper reviews the growth, characterization and device applications of self-assembled InAs/InP(1 0 0) quantum dots (QDs) formed by MOVPE. The problematic As/P exchange reaction during QD growth is suppressed by the insertion of a GaAs interlayer together with optimum growth conditions. This produces QDs with continuously tunable emission over the 1.55-µm wavelength region for fiber-based telecom applications. Device quality of these QDs is proven by continuous wave lasing at room temperature from the as-cleaved facets of Fabry–Pérot narrow ridge-waveguide lasers implementing widely stacked QDs as gain medium. The low transparency current density of 6 A/cm2 per QD layer and low loss of 4.2 cm-1 are accompanied by a 80-nm wide gain spectrum. The deeply etched QD lasers possess similar threshold current densities as the shallowly etched ones and do not deteriorate with time, revealing that device performance does not suffer from sidewall recombination. This allows the fabrication of mono-mode and more compact devices with small bending radii, as demonstrated by the operation of a QD ring laser with 40-GHz free spectral range. Unpolarized emission from the cleaved side, important for the realization of polarization insensitive semiconductor optical amplifiers, is obtained by close stacking of QDs due to vertical electronic coupling. Sharp exciton–biexciton emission from a single QD around 1.55 µm is observed with clearly resolvable peaks above 70 K, which is required for single photon sources working at liquid nitrogen temperature for fiber-based quantum cryptography systems

1.55-μm range InAs/InP (100) quantum dot telecom devices

Lasing and sharp line emission in the 1.55-µm wavelength region is demonstrated from ensembles and single InAs quantum dots (QDs) embedded in InGaAsP on InP (100) by metalorganic vapor phase epitaxy (MOVPE). Wavelength tuning of the QDs is achieved through the insertion of ultra-thin (1-2 monolayers) GaAs interlayers underneath the InAs QDs. To increase the active volume widely-stacked QD layers are identically reproduced. Closely-stacked QDs reveal unpolarized emission from the cleaved side due to vertical electronic coupling which is important for polarization insensitive semiconductor optical amplifiers. Fabry-Perot narrow ridge-waveguide lasers implementing five layers of widely-stacked QDs as gain medium operate in continuous wave mode at room temperature with low threshold current, low transparency current density of 6 A/cm2 per QD layer, and low loss of 4.2 cm-1, which are accompanied by a 80 nm wide gain spectrum. Device performance does not suffer from sidewall recombination in deeply-etched QD lasers which possess similar threshold currents as shallowly-etched ones and do not deteriorate with time. This allows the fabrication of mono-mode and compact devices with small bending radii, as demonstrated by the operation of a QD ring laser with 40-GHz free spectral range. Micro-PL of single QDs exhibits sharp exciton - biexciton emission around 1.55 µm persisting to temperatures above 70 K; the prerequisite for single photon sources working at liquid nitrogen temperature for fiber-based quantum information and cryptography system