InAs Quantum Dots Samples Research Articles

Research on the photoluminescence of spectral broadening by rapid thermal annealing on InAs/GaAs quantum dots

Photoluminescence (PL) test was conducted to investigate the effect of rapid thermal annealing (RTA) on the optical performance of self-assembled InAs/GaAs quantum dots (QDs) at the temperatures of 16 and 300 K. It was found that after RTA treatment, the PL spectrum of the QDs sample had a large blue-shift and significantly broadened at 300 K. Compared with the as-grown InAs QDs sample, the PL spectral width has increased by 44.68 meV in the InAs QDs sample RTA-treated at 800 °C. The excitation power-dependent PL measurements showed that the broadening of the PL peaks of the RTA-treated InAs QDs should be related to the emission of the ground state (GS) of different-sized InAs QDs, the InAs wetting layer (WL) and the In0.15Ga0.85As strain reduction layer (SRL) in the epitaxial InAs/GaAs layers.

Effect of lattice-mismatch strain on electron dynamics in InAs/GaAs quantum dots as seen by time-domain terahertz spectroscopy

Considering the electron dynamics in a deeper area from the surface is important to improve the efficiency of optoelectronic devices. Potential variations due to InAs quantum dot (QD) growth in the GaAs crystal are investigated via measurements of terahertz electromagnetic waves emitted from the surface. In the pump-energy dependence of the time-domain signal, a phase inversion was observed in the QD sample. In addition, while the signal intensity from the InAs QD sample is maintained in the lower pump energy region, the intensity profile does not show this specific change related to the phase inversion. These results demonstrate that the potential change around QDs caused by lattice-mismatched strain can be examined using observations of the time-domain terahertz signal, which can be used to improve the device performance.

Growth and optical characteristics of InAs quantum dot structures with tunnel injection quantum wells for 1.55 [formula omitted]m high-speed lasers

InP based lattice matched tunnel injection structures consisting of a InGaAs quantum well, InAlGaAs barrier and InAs quantum dots designed to emit at 1.55 μm were grown by molecular beam epitaxy and investigated by photoluminescence spectroscopy and atomic force microscopy. The strong influence of quantum well and barrier thicknesses on the samples emission properties at low and room temperatures was investigated. The phenomenon of a decreased photoluminescence linewidth of tunnel injection structures compared to a reference InAs quantum dots sample could be explained by the selection of the emitting dots through the tunneling process. Morphological investigations have not revealed any effect of the injector well on the dot formation and their size distribution. The optimum TI structure design could be defined.

Influence of GaAsBi Matrix on Optical and Structural Properties of InAs Quantum Dots

InAs/GaAsBi dot-in-well structures were fabricated using gas-source molecular beam epitaxy and investigated for its optical and structural properties. GaAsBi-strained buffer layer and strain reduction layer are both effective to extend the photoluminescence (PL) emission wavelength of InAs quantum dot (QD). In addition, a remarkable PL intensity enhancement is also obtained compared with low-temperature-grown GaAs-capped InAs QD sample. The GaAsBi matrix also preserves the shape of InAs QDs and leads to increase the activation energy for nonradiative recombination process at low temperature. Lower density and larger size of InAs QDs are obtained on the GaAsBi surface compared with the QDs grown on GaAs surface.

Growth optimization of InAs/GaAs quantum dots and performance enhancement of a GaAs tunnel diode by embedding quantum dots for solar cell application

We report the performance enhancement of a molecular beam epitaxy grown GaAs tunnel diode embedded with InAs quantum dots (QDs) for tandem solar cell application, and characterization of tunnel diodes embedded with InAs QDs grown with different growth parameters. Prior to the growth and fabrication of the tunnel diode, InAs QDs were grown under different growth durations and temperatures. The InAs QD samples grown in a temperature range from 480 to 520 °C for a duration of 32 s showed the highest areal fill fraction by InAs QDs. Tunnel diodes embedded with InAs QDs that were grown at various growth conditions were fabricated and characterized. We found that the tunnel diode embedded with InAs QD grown at 520 °C showed the highest peak tunnel current density among all the samples. The enhanced performance of the InAs QD embedded tunnel diode is attributed to the large areal fill fraction produced by the presence of large InAs QDs having high density, which are formed at sufficiently high growth temperature and long growth duration.

Sweeping-rate-dependent photocurrent of GaAs Schottky diode with strain relaxed InAs quantum dots

We demonstrate that the photocurrent of a GaAs Schottky diode can be influenced by the carrier stored in strain relaxed InAs quantum dots (QDs) embedded in the Schottky diode. A potential drop is induced by the charged QDs, and the photocurrent generated from the Schottky diode can be suppressed by the induced potential drop. In this paper, the charging time of the relaxed InAs QDs is obtained from 0.1 to 10 s. So the variation in photocurrent can be detected, if the sweeping rate of applied bias is from 10 to 0.1 V/s. Two kinds of QD samples, relaxed and non-relaxed InAs QDs, are compared, and we found that the photocurrent is obviously influenced in the relaxed InAs QD sample. A equivalent RC circuit modal also is provided to analyze the formula of the photocurrent, and the analysis agrees with the results of measurements. This study is advantageous for the investigation of QD memory devices.

Extraction efficiency enhancement of single InAs quantum dot emission through light scattering on the Au nanoparticles

Single semiconductor quantum dots (QDs) have been considered as the promising solid-state single photon sources. To obtain bright quantum sources, the key issue is to enhance extraction efficiency of the QD emission, which is challenging since QDs normally emit isotropically in a high refractive index material. In this article, we investigate the influence of Au nanoparticles on the QD photoluminescence (PL) extraction efficiency based on the techniques of optically positioned QDs and single QD emission detection. The InAs QD samples studied are grown using the molecular beam epitaxy on a (001) GaAs substrate. The sample consists of, in sequence, a 200 nm GaAs buffer layer, a 100 nm AlAs sacrificed layer, a 30 nm GaAs, a QD layer, and a 100 nm GaAs cap layer. The QD sample is mounted in a cryostat cooled down to 5 K, and excited by illumination of a 640 nm diode laser (CW or pulsed with a repetition frequency of 80 MHz). Excitation laser beam is focused to an approximately 2 μm spot on the sample using a microscope objective (NA : 0.5) which is mounted on a nanocube XYZ piezo nanopositioning stage with a scanning range of 100×100×100 μm3. The QD PL is collected using the same objective and measured using a 0.5 m focal length monochromator equipped with a silicon charge-coupled device (CCD). The PL decay measurements are performed using a silicon avalanche photodiode (APD) and a time-correlated single-photon counting (TCSPC) board.#br#In order to study the influence of different environments surrounding the QDs on the spontaneous emission rate and the extraction efficiency, the same QD emissions are measured under the conditions that: (1) A typical QD is at first chosen and optically positioned and then its emission is measured. (2) A GaAs layer containing the QDs is lifted off from the as-grown sample by an AlAs sacrificed layer and placed on the Au film with or without Au nanoparticles. (3) Optical measurements are carried out to obtain the QD emission intensity. This technique enables us to compare the same QD emission intensity for the as-grown QD sample, which is placed on the Au film or on the Au nanoparticles.#br#In summary, it is found that the measured QD emission intensity increases up to 6 times that of the original for the QD placed on the Au nanoparticles, otherwise it is only doubled for the QD placed on the Au film. The time-resolved PL measurements show that the QDs have nearly the same decay time for the QDs in different environments, implying that the QD spontaneous emission rate has not been changed. Therefore, the enhanced PL is due to the increase of extraction efficiency. The physical mechanism underlying the Au nanoparticles-induced PL enhancement is attributed to the trapped QD emission light within the sample and scattered again by Au nanoparticles and collected by the microscopy objective.

Photoluminescence from plasmon-enhanced single InAs quantum dots

Photoluminescences (PLs), time-resolved PL spectra, and PL intensities each as a function of excitation power from plasmon-enhanced single InAs quantum dots (QDs) are measured for studying the effect of photoluminescence enhancement at a low temperature of 5 K. The 5 nm gold films are deposited on the surface of InAs QD sample by using electron beam evaporation technique, which form nano-gold island membrane structures. It is found that the gold island film is conducive to the enhancement of QD PL intensity and the maximal PL intensity increases up to about 5 times the PL intensity without gold island film. The physical mechanism of the PL increase is that the gold island film nanostructure can improve the QD PL collection efficiency which is very important for realizing the bright single photon sources.

As 차단 시간 변화에 의한 InAs 양자점의 광학적 특성

Arsenic interruption growth (AIG)법을 이용하여 GaAs 기판에 성장한 InAs 양자점(quantum dots, QDs)의 광학적 특성을 PL (photoluminescence)과 time-resolved PL을 이용하여 분석하였다. AIG법은 InAs 양자점 성장 동안 In 공급은 계속 유지하면서 셔텨(shutter)를 이용해서 As 공급과 차단을 조절하는 방법이다. 본 연구에서는 As 공급과 차단을 1초(S1), 2초(S2), 또는 3초(S3) 동안 반복하여 성장한 InAs QDs과 As 차단 없이 성장한 기준시료(S0)를 사용하였다. AIG법으로 성장한 시료들의 PL 세기는 기준시료보다 모두 강하게 나타나고, As 차단 시간에 따라 PL 피크는 적색이동(redshifted) 또는 청색이동 (blueshifted)하여 나타났다. 기준시료 S0의 PL 피크와 비교하였을 때 S1의 PL 피크의 적색이동은 양자점 평균 길이가 S0보다 증가하였기 때문이며, S3의 청색이동은 양자점 평균 길이가 S0보다 감소하였기 때문이다. AIG법으로 성장한 QDs 시료들의 PL 세기의 증가는 cluster의 감소, 양자점 밀도의 증가, 균일도의 향상, 종횡비(aspect ratio) 향상으로 설명된다. 온도에 따른 PL 세기와 PL 피크 에너지, PL 소멸 시간과 발광 파장에 따른 PL 소멸 시간을 측정하였다. As 공급과 차단을 2초로 하였을 때 cluster는 전혀 나타나지 않았고 양자점의 밀도는 증가하였으며 균일도와 종횡비도 향상되었다. 또한 S2는 가장 강한 PL 세기와 가장 긴 소멸 시간을 나타내었다. 이러한 결과는 AIG법을 이용하여 InAs 양자점의 크기, 조밀도, 균일도, 종횡비 등을 조절하여 원하는 파장대의 양자점을 성장할 수 있으며 발광 특성도 향상시킬 수 있음을 확인하였다. The optical properties of InAs quantum dots (QDs) grown on GaAs substrates grown by molecular beam epitaxy have been studied using photoluminescence (PL) and time-resolved PL measurements. InAs QDs were grown using an arsenic interruption growth (AIG) technique, in which the As flux was periodically interrupted by a closed As shutter during InAs QDs growth. In this study, the shutter of As source was periodically opened and closed for 1 (S1), 2 (S2), or 3 s (S3). For comparison, an InAs QD sample (S0) without As interruption was grown in a pure GaAs matrix for 20 s. The PL intensity of InAs QD samples grown by AIG technique is stronger than that of the reference sample (S0). While the PL peaks of S1 and S2 are redshifted compared to that of S0, the PL peak of S3 is blueshifted from that of S0. The increase of the PL intensity for the InAs QDs grown by AIG technique can be explained by the reduced InAs clusters, the increased QD density, the improved QD uniformity, and the improved aspect ratio (height/length). The redshift (blueshift) of the PL peak for S1 (S3) compared with that for S0 is attributed to the increase (decrease) in the QD average length compared to the average length of S0. The PL intensity, PL peak position, and PL decay time have been investigated as functions of temperature and emission wavelength. S2 shows no InAs clusters, the increased InAs QD density, the improved QD uniformity, and the improved QD aspect ratio. S2 also shows the strongest PL intensity and the longest PL decay time. These results indicate that the size (shape), density, and uniformity of InAs QDs can be controlled by using AIG technique. Therefore the emission wavelength and luminescence properties of InAs/GaAs QDs can also be controlled.

Electron Emission Properties of Nitrogen-Induced Localized Defects in InAsN/GaAs Quantum Dots

The electron-emission properties of nitrogen-induced (N-induced) localized defects in InAsN/GaAs quantum dots (QDs) are investigated in detail by capacitance–voltage (C–V) profiling and bias-dependent deep-level transient spectroscopy (DLTS). The incorporation of nitrogen (N) into InAs QDs is shown to produce localized defects near QDs and threading-dislocation-related defects in the top GaAs layer. The threading dislocation is associated with an electron-emission energy of approximately 0.648 eV and emission from the sample surface toward the QDs. The electron-emission energy from the QDs associated with the localized defects increases from 0.19 to 0.36 eV, indicating that both types of defect near QDs have low electron emission energies. Therefore, the change in emission energy is attributable to the defects across the QD interface where a band offset exists. The C–V profile at 300 K shows extended carrier depletion near the QDs. As ac frequency increases, an electron-emission peak emerges at the QDs; this peak is followed by another prominent peak, suggesting that the localized defect that is responsible for this latter peak has an energy below the QD electron ground state. On the basis of a C–V profile simulation, this defect is located at the QD at the observed emission energy below the GaAs conduction band, 360 meV. A comparison with InAsN QD and strain relaxation InAs QD samples reveals that the localized defect arises from a nitrogen alloy fluctuation in the QD. The energy location of this defect reveals a possibility that incorporated N is associated with a particular mode.

Marked reduction in photocarrier lifetime by erbium doping into self-assembled InAs quantum dots embedded in strain-relaxed InGaAs barriers

Effects of erbium doping on photocarrier lifetime have been investigated for self-assembled InAs quantum dots (QDs) embedded in strain-relaxed In0.35Ga0.65As barriers grown on (100) GaAs substrates by molecular beam epitaxy. Time-resolved transmission change measurements were performed on 20-layer stacks of the Er-doped InAs QDs at room temperature using 0.1ps laser pulses with the center wavelength of 1.5μm. Fast and slow decay components were observed in the temporal profile of each Er-doped InAs QD sample. The slow decay component attributed to the radiative recombination process in the QDs was well suppressed by increasing Er-doping density. Moreover, the decay time of the fast component due to the nonradiative process was markedly reduced by the incorporation of Er dopants during the QD formation. A decay time of 3.5ps was obtained for the Er-doped InAs QD sample with a sheet density of incorporated Er dopants per QD layer of 2.7×1013cm−2.

Neutralization of positively charged excitonic state in single InAs quantum dot by Si delta doping

Positively charged excitonic state in single InAs quantum dot (QD) has been neutralized by Si delta doping and the optical properties of the fabricated samples are characterized by micro-photoluminescence measurements (μ-PL) at low temperature. An InAs QD sample having dominant emissions from positively charged excitonic states is prepared for a reference. By optimizing Si delta doping conditions, positively charged QDs are neutralized successfully and distinctive emissions from neutral exciton and biexciton from single QDs are achieved. For excessive doping condition, μ-PL spectra show optical degradation of lowering of peak intensity and broadening of peak width as doping concentration increases.

Mn-including InAs quantum dots fabricated by Mn implantation

Mn-including InAs quantum dots (QDs) were fabricated by Mn-ion implantation and subsequent annealing. The optical, compositional, and structural properties of the treated samples were analyzed by photoluminescence (PL) and microscopy. Energy dispersive X-ray (EDX) results indicate that Mn ions diffused from the bulk GaAs into the InAs QDs during annealing, and the diffusion appears to be driven by the strain in the InAs QDs. The temperature dependence of the PL of Mn-including InAs QD samples exhibits QDs PL characteristics. At the same time, the heavy Mn-including InAs QD samples have ferromagnetic properties and high T c.

The effect of the inserted AlGaAs films on the behaviors of InAs quantum dot detector

Two InAs quantum dot samples have been grown by the solid source molecular beam epitaxy (MBE) and fabricated to detectors. AlGaAs thin films have been inserted into the source region for one of the two devices. The structural features of the two samples have been studied by using the transmission electron microscope (TEM). The photoelectric properties of them have been measured by the photoluminescence (PL) and photocurrent (PC) spectra. The experimental results indicated that the AlGaAs films have profound effects on the properties of the detector. According to the calculations based on effective mass approximation, the origins of the photocurrent peaks of the two devices have been identified.

High-temperature growth of Mn-irradiated InAs quantum dots

We fabricated Mn-irradiated InAs quantum dot (QD) structures at 500 °C. In the case of Mn irradiation on InAs QDs without As, the terraces were observed around dots by an atomic force microscope (AFM). It is believed that Mn atoms adhere to InAs QDs and MnAs is formed. Furthermore, we measured micro-photoluminescence from such Mn-irradiated InAs QD samples under magnetic fields. Clear Zeeman splitting was observed at 2.9 K. The estimated absolute values of the exciton g factor were 2.4–3.8.

Growth and characterization of Si-doped self-assembled InAs quantum dots

Si-doped self-assembled InAs quantum-dot samples were grown, and the influences of doping on the structural and optical properties of quantum dots were investigated. As Si doping concentrations increased, increased size, reduced areal density, and broadened size distributions of quantum dots were observed. Photoluminescence spectra of Si-doped quantum dots showed that the peaks of ground state transitions shifted with varied doping concentrations while, the peak positions of wetting layers were unchanged. Photoluminescence intensities of excited state transitions of Si-doped quantum dots and of wetting layers were reduced as Si concentration increased.

Bandgap engineering of self-assembled InAs quantum dots with a thin AlAs barrier

We investigate the effects of a thin AlAs layer with different position and thickness on the optical properties of InAs quantum dots (QDs) by using transmission electron microscopy and photoluminescence (PL). The energy level shift of InAs QD samples is observed by introducing the thin AlAs layer without any significant loss of the QD qualities. The emission peak from InAs QDs directly grown on the 4 monolayer (ML) AlAs layer is blueshifted from that of reference sample by 219 meV with a little increase in FWHM from 42–47 meV for ground state. In contrast, InAs QDs grown under the 4 ML AlAs layer have PL peak a little redshifted to lower energy by 17 meV. This result is related to the interdiffusion of Al atom at the InAs QDs caused by the annealing effect during growing of InAs QDs on AlAs layer.

Time-resolved photoluminescence spectroscopy of InAs quantum dots on InP with various InAlGaAs barrier thicknesses

The Optical characteristics of InAs quantum dots (QDs) embeded in InAlGaAs on InP have been investigated by photoluminescence (PL) spectroscopy and time-resolved PL. Four different QD samples are grown by using molecular beam epitaxy, and all the QD samples have five-stacked InAs quantum dot layers with a different InAlGaAs barrier thickness. The PL yield from InAs QDs was increased with an increase in the thickness of the InAlGaAs barrier, and the emission peak positions of all InAs QD samples were measured around 1.5 μm at room temperature. The decay time of the carrier in InAs QDs is decreased abruptly in the QD sample with the 5 nm InAlGaAs barrier. This feature is explained by the tunneling and coupling effect in the vertical direction and probably defect generation.

Structural and optical properties of GaAs/AlGaAs superlattice layer on InAs quantum dots

We used photoluminescence (PL), photoreflectance (PR) spectroscopy and transmission electron microscopy (TEM) to investigate the effects of high potential barriers on the optical and structural characteristic of InAs quantum dots (QDs). A sample with regular InAs QDs on GaAs was grown as a reference using molecular beam epitaxy. Another InAs QD sample was embedded in a single AlGaAs barrier. A sample with a GaAs/AlGaAs superlattice barrier was compared with the single AlGaAs layer sample. Our results showed that the emission wavelength of the QDs was effectively tailored by the high potential barriers. The optical properties of the sample with QDs embedded in GaAs/AlGaAs superlattices were better than those of the sample with the QDs embedded in a single layer of AlGaAs. We believe that this was because the GaAs/AlGaAs superlattice is effective in preventing the generation of defects.

Intersublevel Relaxation Dependence of Carrier Hopping in Self-Organized InAs Quantum Dot Heterostructures

The temperature dependence of the photoluminescence (PL) emission spectra of self-organized InAs/GaAs quantum dots (QDs) grown under different growth conditions in the range 20-300K has been investigated. Three InAs QD samples were grown on (100) 2º-tilted toward (111)A Si-doped GaAs substrates by metal-organic chemical vapour epitaxy (MOVPE), with various size uniformities and dot densities. Observing the measured PL spectra at 20K, the differences caused by size uniformities among the three samples were obvious. The PL spectra were simulated with rate equations, taking into account the carrier relaxation between the first excited state and the ground state. Interestingly, the calculated relaxation lifetimes at 20K were 198ps, 139ps and 54ps for the samples. The temperature dependent PL spectra were also simulated using the same model. Based on the calculated values of temperature dependent relaxation lifetimes, the differences in changes with temperature among the three samples are discussed. The results are consistent with the thermal redistribution effect.