Growth Of Site-controlled Quantum Dots Research Articles

Epitaxial growth and characterization of multi-layer site-controlled InGaAs quantum dots based on the buried stressor method

We report on the epitaxial growth, theoretical modeling, and structural as well as optical investigation of multi-layer, site-controlled quantum dots fabricated using the buried stressor method. This deterministic growth technique utilizes the strain from a partially oxidized AlAs layer to induce site-selective nucleation of InGaAs quantum dots. By implementing strain-induced spectral nano-engineering, we achieve spectral control of emission and a local increase in the emitter density. Furthermore, we achieve a threefold increase in the optical intensity and reduce the inhomogeneous broadening of the ensemble emission by 20% via stacking three layers of site-controlled emitters, which is valuable for using the SCQDs as a gain medium in microlaser applications. Our optimization of site-controlled growth of quantum dots enables the development of high-β microlasers with increased confinement factor.

Precisely ordered Ge quantum dots on a patterned Si microring for enhanced light-emission

Semiconductor microcavities can greatly enhance the light-emission of embedded quantum dots (QDs). Here, a new route toward the microcavity-QD system by fabricating microcavities followed by growing ordered QDs on a patterned microresonator is proposed, which keeps QDs from being etched. Self-assembled Ge QDs prefer to form at the rims of Si microrings or microdisks. The Ge QDs on the pit- or groove-patterned microring resonator (MRR) show better size uniformity and position accuracy. These features are explained by the evolutions of surface morphology and surface chemical potential distribution. Sharp photoluminescence peaks in the telecommunication band with the quality factors in the range of 450–850 from groove-patterned MRR are observed at 295 K due to efficient overlap between Ge QDs and resonant modes. Our schemes shed light on the exactly site-controlled growth of QDs on micro- and nano-structures, which further facilitates the investigation of light-matter interactions.

Laser induced nano-patterning with atomic-scale thickness on an InAs/GaAs surface

Nano-patterned substrates fabricated by different techniques have been widely applied in high performance semiconductor devices. For the influence of surface morphology on semiconductor electronic properties and epitaxy growth, there is an increasing interest to realize atomic-scale surface modification by a simple and effective method. In this study, laser induced nano-patterning with atomic-scale thickness on an InAs/GaAs surface was studied in both atmosphere and vacuum environments. Periodic nano-grooves with an average depth of 1 to 2 atomic layers were fabricated by focused laser spot scanning in the air. The depth and width of nano-grooves increase with the laser energy intensity. The result of nano-patterning is attributed to atom desorption stimulated by photon-induced electronic excitation. To explore the situation in the vacuum, in situ two-beam laser interference was applied during InAs/GaAs sample MBE growth. Periodic InGaAs nano-islands were fabricated, which show significant influence on subsequent crystal growth. The formation of ordered InAs quantum dots agreeing with the atomic layer nano-pattern demonstrates the potential application of the technique in site-controlled quantum dot growth.

Resonance fluorescence of a site-controlled quantum dot realized by the buried-stressor growth technique

Site-controlled growth of semiconductor quantum dots (QDs) represents a major advancement to achieve scalable quantum technology platforms. One immediate benefit is the deterministic integration of quantum emitters into optical microcavities. However, site-controlled growth of QDs is usually achieved at the cost of reduced optical quality. Here, we show that the buried-stressor growth technique enables the realization of high-quality site-controlled QDs with attractive optical and quantum optical properties. This is evidenced by performing excitation power dependent resonance fluorescence experiments at cryogenic temperatures showing QD emission linewidths down to 10 μeV. Resonant excitation leads to the observation of the Mollow triplet under CW excitation and enables coherent state preparation under pulsed excitation. Under resonant π-pulse excitation we observe clean single-photon emission associated with g(2)(0) = 0.12 limited by non-ideal laser suppression.

Electrically driven single photon source based on a site-controlled quantum dot with self-aligned current injection

Electrical operation of single photon emitting devices employing site-controlled quantum dot (QD) growth is demonstrated. An oxide aperture acting as a buried stressor structure is forcing site-controlled QD growth, leading to both QD self-alignment with respect to the current path in vertical injection pin-diodes and narrow, jitter-free emission lines. Emissions from a neutral exciton, a neutral bi-exciton, and a charged exciton are unambiguously identified. Polarization-dependent measurements yield an exciton fine-structure splitting of (84 ± 2) μeV at photon energies of 1.28–1.29 eV. Single-photon emission is proven by Hanbury Brown and Twiss experiments yielding an anti-bunching value of g(2)(0) = 0.05 under direct current injection.

Spatial point analysis of quantum dot nucleation sites on InAs wetting layer

We perform spatial point analysis of InAs quantum dot (QD) nucleation sites and surface reconstruction domain patterns on an InAs wetting layer to investigate QD nucleation mechanisms in Stranski-Krastanow growth mode. An InAs wetting layer on a GaAs(001) substrate has been observed at 300 °C by using in situ scanning tunneling microscopy (STM) preceding QD formation. A nearest-neighbor analysis of the STM images finds that the point pattern of QD precursors is similar to that of (1 × 3)/(2 × 3) surface reconstruction domains which are specific to Ga-rich fluctuation. This provides the evidence that InAs QD nucleation is induced by Ga-rich fluctuation within an InAs wetting layer, as a technical implication for site-controlled QD growth for various QD devices.

Single site-controlled In(Ga)As/GaAs quantum dots: growth, properties and deviceintegration

Results obtained by an advanced growth of site-controlled quantum dots (SCQDs) onpre-patterned nanoholes and their integration into both photonic resonators andnanoelectronic memories are summarized. A specific technique has been pursuedto improve the optical quality of single SCQDs. Quantum dot (QD) layershave been vertically stacked but spectrally detuned for single SCQD studies.Thereby, the average emission linewidth of single QDs could be reduced from2.3 meV for SCQDs in a first QD layer close to the etched nanoholes down to 600 µeV in the third InAs QD layer. Accurate SCQD nucleation on large QDdistances is maintained by vertical strain induced QD coupling throughoutthe QD stacks. Record narrow linewidths of individual SCQDs down to∼110 µeV have been obtained. Experiments performed on coupled photonic SCQD–resonator devicesshow an enhancement of spontaneous emission. SCQDs have also been integrateddeterministically in high electron mobility heterostructures and flash memory operation atroom temperature has been observed.

Lithographic alignment to site-controlled quantum dots for device integration

We report on a scalable fabrication technology for devices based on single quantum dots (QDs) which combines site-controlled growth of QDs with an accurate alignment procedure. Placement of individual QDs and corresponding device structures with a standard deviation of around 50nm from the target position was achieved. The potential of the technology is demonstrated by fabricating arrays of mesas, each containing one QD at a defined position. The presence of single, optically active QDs in the mesas was probed by scanning microphotoluminescence of the mesa arrays.

Site control of InAs quantum dots on a patterned InP surface: As/P exchange reactions

In this paper, we present the effect of annealing temperature and annealing time on InAs site-controlled quantum dot growth. Individual InAs quantum dots formed by self-assembling have been positioned into holes, created by partial overgrowth of electron beam induced nano-carbon deposits by metal organic vapor phase epitaxy. As/P exchange reactions produce material sufficient for selective dot nucleation in the holes. Results, showing that As/P exchange reactions occur even when capping the dots with InP are presented.