GaNAs Strain-compensating Layer Research Articles

Multilayer InAs Quantum Dot with GaNAs Strain Compensation Layers Partly Inserted in a Thin Spacer Layer

Multilayer InAs quantum dot with a thin spacer prepared using a GaNAs strain compensation layer was investigated by metalorganic chemical vapor deposition. The GaNAs tensile strained layer was inserted partly in the spacer without contacting with the compressively strained InAs dot and GaInAs cover layer. The stacking number of up to 5 with a thin spacer of 18 nm was realized at a wavelength of 1.4 µm without severe degradation of optical quality although a slight dot size increase in the upper layer was confirmed. The result indicates the advantageousness of GaNAs for a thin spacer structure of the multilayer quantum dot.

Multilayer InAs Quantum Dot with GaNAs Strain Compensation Layers Partly Inserted in a Thin Spacer Layer

Multilayer InAs quantum dot with a thin spacer prepared using a GaNAs strain compensation layer was investigated by metalorganic chemical vapor deposition. The GaNAs tensile strained layer was inserted partly in the spacer without contacting with the compressively strained InAs dot and GaInAs cover layer. The stacking number of up to 5 with a thin spacer of 18 nm was realized at a wavelength of 1.4 µm without severe degradation of optical quality although a slight dot size increase in the upper layer was confirmed. The result indicates the advantageousness of GaNAs for a thin spacer structure of the multilayer quantum dot.

Growth of multi-stacked InAs/GaNAs quantum dots grown with As2 source in atomic hydrogen-assisted molecular beam epitaxy

Abstract We have investigated the effect of using As 2 source on the self-assembly process of 5 layer stacked InAs quantum dots (QDs) on GaAs(0 0 1) grown by atomic hydrogen-assisted molecular beam epitaxy. The deposition thickness of each QD layer was varied from 1.32 to 2.32 monolayers (MLs), and InAs QDs were embedded by a GaNAs strain-compensating layer (SCL). By using As 2 , high-density QDs with higher aspect ratio were formed during the stage of QD formation. A mono-modal size distribution with size fluctuation in diameter of 9.2% was obtained for As 2 sample, which was better than that of 13.6% obtained for As 4 sample. On the other, As 4 sample showed a bimodal size distribution in the initial stage of QD formation. The size distribution gradually improved with increasing InAs deposition and eventually saturated to become larger QDs with a mono-modal size distribution for As 4 sample. The saturated QDs exhibited almost the same PL properties emitting at around 1100 nm with a narrow linewidth of 40 meV at 77 K for both As 2 and As 4 samples.

Optical studies on InAs/InGaAs/GaNAs strain-compensated quantum dots grown on GaAs (0 0 1) by molecular beam epitaxy

We have investigated the growth of 10 stacked layers of self-assembled InAs quantum dots (QDs) on GaAs (0 0 1) substrates, which were embedded in a combined set of a GaNAs strain-compensating layer (SCL) and an InGaAs strain-reducing layer (SRL). The internal compressive strain induced by each InAs QD layer was compensated by a tensile strain due to a GaNAs SCL. Consequently, the photoluminescence (PL) measured at 30 K showed a narrower linewidth of 60.3 meV for the sample with GaN 0.008As 0.992 SCL compared to 94.2 meV for InAs/GaAs uncontrolled sample due to an improved QD size uniformity. In order to reduce the nominal lattice mismatch at the heterointerface, we propose to insert an InGaAs SRL between the InAs QD layer and GaNAs SCL. We observed a PL peak redshift up to 1230 nm at room temperature, and increased PL intensity for InAs QD/InGaAs SRL/GaNAs SCL samples.

Reduction of spacer layer thickness of InAs quantum dots using GaNAs strain compensation layer

Emission and shape characteristics of the InGaAs covered InAs quantum dots with GaNAs strain compensation layers (SCLs) are investigated, focusing on the reduction of the spacer thickness for device applications. Using the GaNAs SCL, the suppression of inhomogeneous emission broadening induced by the compressive strain from lower dot layers was confirmed with the suppression of increase in the dot size of upper dot layers. This result is effective for the suppression of the spacer thickness.

Optical properties of multi-stacked InAs/GaNAs strain-compensated quantum dots

Abstract Structural and optical properties of multi-stacked self-assembled InAs quantum dots (QDs) on GaAs (0 0 1) substrates have been investigated, for which dilute nitride GaN x As 1− x layers were used as strain-compensation layers (SCLs). The growth was achieved by atomic hydrogen-assisted radio frequency (RF)-molecular beam epitaxy. The high-quality QD structures were maintained without generation of coalesced islands and dislocations even after 20 layers of stacking. The photoluminescence (PL) peak showed an increasing redshift up to 1.2 μm at room temperature with increasing N composition up to 1.0% in GaNAs as a result of the lowering of quantum confinement energy. Furthermore, the PL showed a bimodal size distribution-like feature. The temperature dependence of PL characteristics showed a minimum linewidth at an intermediate temperature range of ∼100 K, and existence of the two components obeying the Varshni law. Such behavior can be explained by the dynamics of thermally activated carriers that migrate or tunnel from the smaller-sized QDs to larger QDs via wetting layers. The main reason for the anomalous PL characteristics measured for InAs QDs embedded in GaNAs SCLs is possibly the fluctuations of potential energy in GaNAs layers.

MBE growth of InAs self-assembled quantum dots embedded in GaNAs strain-compensating layers

We fabricated self-assembled InAs quantum dots (QDs) embedded with a combined set of a GaNAs strain-compensating layer (SCL) and an InGaAs strain-reducing layer (SRL) by using atomic hydrogen-assisted molecular beam epitaxy (H-MBE) with a RF plasma nitrogen source. By inserting an InGaAs SRL between the InAs QD layer and GaNAs SCL, we were able to achieve a significant improvement of optical properties. A 1.3 μ m -range photoluminescence (PL) emission was clearly obtained at 300 K from QDs embedded in a 5 nm-thick In 0.15Ga 0.85As SRL followed by a 20 nm-thick GaN 0.008As 0.992 SCL. Further, PL emission from the first excited state of QDs was also observed under a high excitation intensity of ∼ 20.0 W / cm 2 .

Multiple stacking of self-assembled InAs quantum dots embedded by GaNAs strain compensating layers

We have investigated a growth technique to realize high-quality multiple stacking of self-assembled InAs quantum dots (QDs) on GaAs (001) substrates, in which GaNxAs1−x dilute nitride material was used as a strain compensation layer (SCL). The growth was achieved by atomic hydrogen-assisted rf molecular beam epitaxy, and the effect of strain compensation was systematically investigated by using high-resolution x-ray diffraction measurements. By controlling the net average lattice strain to a minimum by covering each QD layer with a 40-nm-thick GaN0.005As0.995 SCL, we obtained a superior QD structure with no degradation in size homogeneity. Further, no dislocations were generated even after 30 layers of stacking, and the area density of QDs amounted to as high as 3×1012cm−2. The photoluminescence peak linewidth was improved by about 22% for QDs embedded in GaNAs SCLs as the accumulation of lattice strain with increasing growth of QD layers was avoided, which would otherwise commonly lead to degradation of size homogeneity and generation of dislocations.

Influence of GaNAs strain compensation layers upon annealing of GaIn(N)As/GaAs quantum wells

GaIn(N)As/GaAs and GaIn(N)As/GaNAs/GaAs quantum well samples, with and without GaNAs strain-compensating layers (SCL), were grown on GaAs (001) substrates by molecular beam epitaxy. Photoluminescence (PL) was used to study the effects of the GaNAs SCL on the properties of the Ga(In)NAs QWs upon annealing. It is found that an extra blue-shift (Δ E = 5.2 meV) in the PL emission from the GaInNAs QW sample at the initial annealing stage ( t ann = 40 s) was induced by the GaNAs SCLs. However, for the GaInAs QW sample, the blue-shift induced by GaNAs SCL is only 1.1 meV. As the annealing time was increased, the blue-shift of both GaInNAs and GaInAs QWs showed saturations at 16 meV and 8 meV, respectively. The PL blue-shifts were much enhanced by inserting GaNAs SCLs showing a non-saturable behavior. X-ray diffractions from the strain compensated GaIn(N)As QWs before and after annealing show no N atom diffusion but Ga/In atom interdiffusion across the QW interfaces. The Ga/In atom interdiffusion caused by annealing was also confirmed by high-resolution transmission electron microscopy from the GaInNAs/GaAs QW sample.

Influence of GaNAs strain-compensation layers on the optical properties of GaIn(N)As∕GaAs quantum wells upon annealing

Ga In ( N ) As ∕ Ga As and GaIn(N)As∕GaNAs∕GaAs quantum well (QW) samples, with and without GaNAs strain-compensating layers (SCLs), were grown on GaAs (001) substrates by molecular beam epitaxy. Photoluminescence (PL) was used to study the effects of the GaNAs SCL on the properties of the Ga(In)NAs QWs upon annealing. We observed that the insertion of GaNAs SCL produced a distinct increase in the PL blueshift as a function of annealing time. X-ray diffraction from the strain-compensated GaIn(N)As QWs before and after annealing showed no N atom diffusion, but exhibited Ga–In atom interdiffusion across the QW interfaces. We compared the effects of the GaNAs SCL on the PL blueshift with those of the SiO2 encapsulant upon annealing. The increased PL blueshift caused by the GaNAs SCL for tann⩽40s is attributed to the further GamIn4−m–N (0⩽m⩽4) changes due to greater local strain caused by GaNAs (SCL) quantum barriers as compared with GaAs barriers. For tann>40s, the nonsaturable blueshift caused by GaNAs SCL is attributed to defect-assisted (especially, Ga vacancies) Ga∕In interdiffusion, since the density of Ga vacancy defects in the GaNAs SCLs is quite high.

Long wavelength InAs self-assembled quantum dots embedded in GaNAs strain-compensating layers

We investigated the effect of GaNAs strain-compensating layers (SCLs) on the properties of InAs self-assembled quantum dots (QDs) grown on GaAs (0 0 1) substrates. The GaNAs material can be used as SCL thereby minimizing the net strain, and thus is advantageous for multi-stacking of InAs QDs structures and achieving long wavelength emission. The emission wavelength of InAs QDs can be tuned by changing the nitrogen (N) composition in GaNAs SCLs due to both effects of strain compensation and lowering of potential barrier height. A 1.3 μ m photoluminescence emission at 77 K was clearly observed for sample with GaN 0.024 As 0.976 SCL. Further, we observed an improvement of optical properties of InAs QDs by replacing the more popular GaAs embedding layers with GaNAs SCLs, which is a result of decreasing non-radiative defects owing to minimizing the total net strain.

Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers

Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs.

GaNAs as Strain Compensating Layer for 1.55 µm Light Emission from InAs Quantum Dots

GaNAs strain-compensating layers (SCLs) are applied to bury InAs quantum dots (QDs) grown on GaAs substrates. The main idea is the compensation of the compressive strain induced by InAs QDs with the tensile strain in the GaNAs SCLs to keep the total strain of the system minimum. The application of the GaNAs SCLs resulted in a systematic shift of photoluminescence (PL) peaks of the InAs QDs toward the longer wavelengths with the increase of the nitrogen (N) composition in GaNAs, and luminescence at a wavelength of 1.55 µm has been achieved from the InAs QDs for the N composition of 2.7% in the GaNAs SCL. This result is promising for the application of GaNAs SCL for InAs-QDs-based long-wavelength light sources for optical-fiber communication systems.

III–V–N-related quantum structures for 1.5 [micro sign]m emission

Two kinds of III–V–N related quantum structures grown on GaAs are proposed, which have the capability to emit in the 1.5 µm wavelength range. GaAsNSe is a new quaternary with high residual electron concentrations. It is shown that GaAsNSe/GaAs superlattices, with structural optimisation, give bright luminescence around 1.5 µm at room temperature. A second structure is InAs quantum dots (QDs) grown on (001) GaAs. Instead of a conventional GaAs capping layer, a GaNAs strain-compensating layer (SCL) is proposed to minimise net compressive strain induced by InAs QDs. The application of a GaNAs SCL to cap InAs QDs improves the homogeneity and optical quality of the InAs QDs by the compensation of net strain. It is shown that 1.5 µm emission from InAs QDs is made possible by increasing the N composition in the GaNAs SCL.