Growth of Columnar Quantum Dots by Metalorganic Vapor-Phase Epitaxy for Semiconductor Optical Amplifiers

Abstract

Growth of polarization-controlled quantum dots (QDs) by metalorganic vapor-phase epitaxy for semiconductor optical amplifiers (SOAs) is reported. Columnar QDs with small lateral sizes and high aspect ratios were formed using low growth temperatures and highly tensile-strained barriers. Dominant polarization sensitivities of columnar QDs were changed from the transverse-electric (TE) mode to the transverse-magnetic (TM) mode by controlling the heights of columnar QDs and tensilestrained barriers. TM-gain-dominant-QD SOAs were fabricated. A TM-mode gain of 17.3 dB was obtained at a wavelength of 1.55 mm. Polarization dependent gain was tuned by barrier thickness and reduced to 2.5 dB.

Study of multiple-stacking growth of 1.55μm InAs columnar quantum dots with modulated tensile-strained InGaAsP barrier layers

“…3 shows the PL spectra of 12-fold type 1 CQDs for which the tensile-strains are 0.4%, 0.6%, 0.8% and 1.4%. As the tensile strain of the barrier layers increases, the PL spectra become blueshifted since the strain condition of the InAs QDs changes from biaxial to hydrostatic, the bandgap energy of the CQDs becomes larger with the increasing barrier layer tensile-strain [18]. The relationship of the CQD PL peak wavelength to the amount of tensile strain in the barrier layers is shown in the inset of Fig.…”

“…These devices were demonstrated using self-assembly formed QDs grown by Stranski-Krastanow mode. In order to improve the controllability of QDs, electronically-coupled columnar QDs (CQDs), which are composed of multi-stacked QD layers and thin barrier layers, were proposed [11][12][13][14][15][16][17][18][19]. Since the height and strain of the CQDs depend on the stacking number and the thickness and strain of the barrier layers, emission wavelength and polarization was expected to be changed [11,12].…”

“…Since the height and strain of the CQDs depend on the stacking number and the thickness and strain of the barrier layers, emission wavelength and polarization was expected to be changed [11,12]. Such structure was formed in InAs/GaAs system [11][12][13][14] and in InAs/InP system [15][16][17][18][19], and it was also applied in the SOAs aiming at controlling the polarization [17,18]. Up to date, a high-performance polarization-insensitive QD-SOA operating at 1.55 mm has been reported in InAs/InP system [15].…”

Tuning of polarization sensitivity in closely stacked trilayer InAs/GaAs quantum dots induced by overgrowth dynamics

“…The flexibility in controlling their geometry by means of growth conditions and, in certain cases substrate patterning [2], has stimulated several studies on more complex structures able to add further potentialities to lensshaped or pyramidal nanostructures commonly obtained by the Stranski-Krastanov process. In this context, one relevant physical example are closely stacked quantum dots, either consisting of QD layers separated by a thin GaAs spacer [3][4][5], or without using any GaAs spacer (also known as columnar QDs [6] or quantum posts [7]). In these kinds of nanostructures, the strong compressive biaxial strain component at the center of the typical flat shape dot can be reduced to zero or towards tensile values by increasing the stack height (adding QD layers), thus providing the optical polarization insensitivity desirable for relevant technological applications such as semiconductor optical amplifiers for high speed communication networks [8][9][10].…”

Quantum Dashes and Quantum Rods: Optical Properties and Application Prospects

“…For instance, it was possible to grow strongly in-plane elongated dots or finite size quantum wires (the so-called quantum dashes, QDashes), which have been demonstrated as very efficient light emitters in the near infrared and found their application as the active region of laser diodes for telecommunication [1]. On the other hand, the fabrication of high aspect ratio quantum dots (called columnar quantum dots or quantum rods) has allowed achieving strongly enhanced emission intensity from the structure edge in the TM (transverse magnetic) linear polarization (with respect to the transverse electric, TE), which gives a potential for the realization of fully polarization independent quantum-dot-like semiconductor optical amplifier [2][3][4][5].…”