Effect Of Growth Interruption Research Articles

Effect of growth interruption on Ga(N, As)/Ga(As, Sb)/Ga(N, As) type-II-“W” quantum well heterostructures

Ga(N,As)/Ga(As,Sb)/Ga(N,As) type-II-“W” quantum well heterostructures and Ga(As,Sb)/Ga(N,As) type-II double quantum well heterostructures have been grown by metal organic vapour phase epitaxy (MOVPE) on GaAs-substrate. In particular the influence of growth interruptions on the interface morphology and the nitrogen incorporation efficiency have been studied. Ga(N,As)/Ga(As,Sb)/Ga(N,As) double quantum well structures have been characterized by high resolution x-ray diffraction, scanning transmission electron microscopy and photoluminescence spectroscopy. The internal interfaces were investigated with atomic force microscopy after application of a wet chemical etching technique that allows selective etching of all layers above. We observed a drastic effect of growth interruption duration on the nitrogen incorporation into Ga(N,As): Without growth interruption the nitrogen content was lowered strongly when grown on Ga(As,Sb) QWs. With increasing growth interruption an increase in nitrogen content is visible. The buried Ga(As,Sb) interface first showed a smoothing followed by a subsequent roughening due to the formation of holes of the Ga(As,Sb)-layer with longer growth interruption durations.

Effects of growth interruption on InGaP fabricated via hydride vapor phase epitaxy

Hydride vapor phase epitaxy (HVPE) is a promising technique for reducing the high cost associated with the fabrication of high-performance III–V solar cells. We studied the effects of growth interruption on InGaP single-junction solar cells fabricated via HVPE. Our HVPE reactor contains two growth chambers and a preparation chamber. The preparation chamber is where the substrate waits under AsH3 or PH3 until the gas flows are stabilized in the next growth’s chamber. In this study, we focus on the effects of the distance from the preparation chamber to the substrate (dpre) and the growth interruption time (tGI) on InGaP/InGaP interfaces. Rough interfaces were formed owing to cross-contamination from other chambers for a sample grown with nonoptimized dpre. In contrast, abrupt InGaP/InGaP interfaces were obtained for a sample grown by decreasing dpre. Furthermore, we found that the tGI affects the device performance when switching the dopant gas from DMZn to H2S.

AlGaN multiple quantum wells by PA-MBE for deep UV emission: Effect of growth interruptions

Growth of AlGaN multiple quantum wells by Plasma Assisted-Molecular Beam Epitaxy has been optimized for use in deep ultraviolet light emitting diodes. A series of samples were grown on c-plane sapphire using an AlN buffer layer, an ~1 μm AlGaN layer, followed by 40-pairs of wells and barriers. The III/V flux ratio was varied from near stoichiometric to excess group III and a plasma exposure step was introduced for some samples after the deposition of wells and barriers. The quality of the well-barrier interface was estimated by the number and intensity of X-Ray Diffraction (XRD) superlattice peaks. Our results indicate that interface abruptness is greatly enhanced by the addition of this process step. While the room temperature photoluminescence (PL) intensity increases significantly upon introduction of the interruption after the barrier layer, this effect is reversed with additional interruption after the well layers. Temperature dependent PL measurements show an anomalous variation with increasing temperature with a maxima around 110°-150°C. This is due to photogeneration of e-h pairs in the underlying AlGaN layer and its subsequent recombination in the quantum wells by diffusion through percolative barrier layers with in-plane potential fluctuations. This is arrested at lowest temperatures causing a reduction in PL intensity. The PL intensity ratio I300K/I4K is highest for samples grown under excess group III, but reduces with the addition of the growth interruption step after the barrier layer. Growth under stoichiometric conditions together with dual growth interruptions was found to be optimal, with improved PL properties while maintaining high interface quality.

Effect of growth interruption in 1.55 μm InAs/InAlGaAs quantum dots on InP grown by molecular beam epitaxy

We report the effect of growth interruptions on the structural and optical properties of InAs/InAlGaAs/InP quantum dots using molecular beam epitaxy. We find that the surface quantum dots experience an unintended ripening process during the sample cooling stage, which reshapes the uncapped InAs nanostructures. To prevent this, we performed a partial capping experiment to effectively inhibit structural reconfiguration of surface InAs nanostructures during the cooling stage, revealing that InAs nanostructures first form quantum dashes and then transform into quantum dots via a ripening process. Our result suggests that the appearance of buried InAs/InAlGaAs nanostructures can be easily misunderstood by surface analysis.

Effect of growth interruptions on TiO2 films deposited by plasma enhanced chemical vapour deposition

TiO2 films of ∼300 nm were deposited at low temperature (<140 °C) and pressure (0.4 Pa) using plasma enhanced chemical vapour deposition at the floating potential (Vf) or the substrate self-bias voltage (Vb) of −50 V. The impact of growth interruptions on the morphology, microstructure and optical properties of the films was investigated. The interruptions were carried out by stopping the plasma generation and gas injection once the increase of the layer thickness during each deposition step was about ∼100 nm. In one case of Vf, the films of ∼300 nm exhibit a columnar morphology consisting of a bottom dense layer, an intermediate gradient layer and a top roughness layer. But the growth interruptions result in an increase of the dense layer thickness and a decrease of surface roughness. The film inhomogeneity has been identified by the in-situ real-time evolution of the kinetic ellipsometry (KE) parameters and the modeling process of spectroscopic ellipsometry (SE). The discrepancy of the refractive index measured by SE between bottom and upper layers can be reduced by growth interruptions. In the other case of Vb = −50 V, the films exhibit a more compact arrangement which is homogeneous along the growth direction as confirmed by KE and SE. Both of Fourier transform infrared spectra and X-ray diffraction illustrate a phase transformation from anatase to rutile with the bias of −50 V, and also evidenced on the evolution of the refractive index dispersion curves. And a greatly increase of the refractive indice in the transparent range can be identified. However, the growth interruptions seem to have no influence on the morphology and optical properties in this case.

Effects of growth interruption, As and Ga fluxes, and nitrogen plasma irradiation on the molecular beam epitaxial growth of GaAs/GaAsN core–shell nanowires on Si(111)

We investigate fundamental issues on the growth of GaAs/GaAsN core–shell heterostructure nanowires (NWs) by plasma-assisted molecular beam epitaxy. A Ga catalyst crystallizes during growth interruption at a high As pressure, and afterwards the growth dominantly progresses mainly increasing the NW diameter, thereby forming a wire shell. The shell diameter increases linearly depending on growth time and group III flux, similarly to the growth mechanism of planar layers. The lateral growth rate is 0.19 times lower than the growth rate of planar GaAs on a (100) substrate. At a substrate temperature 570 °C, nitrogen incorporation is inefficient in the shell layer. At a substrate temperature of 430 °C, the nitrogen is effectively introduced under continuous plasma irradiation during the growth of the GaAsN shell, resulting in the introduction of nitrogen within the shell estimated up to about 0.5%.

In situ spectroscopic ellipsometry study of TiO2 films deposited by plasma enhanced chemical vapour deposition

TiO2 thin films of 300–400nm were deposited at low pressure (3mTorr) and temperature (<150°C) on silicon substrates using plasma enhanced chemical vapour deposition with different substrate self-bias voltages (Vb). The impact of growth interruptions on the film characteristics was studied by in situ spectroscopic ellipsometry (SE), scanning electron microscopy (SEM) and X-ray diffraction. The interruptions were carried out by stopping the plasma generation and gas injection once the increase of the layer thickness during each deposition step was about 100nm. Suitable ellipsometric models were built to account for the structural and optical differences among the layers grown at different stages. When no bias is applied or Vb=−10V, the films deposited with and without interruptions are composed of a dense layer near substrate, an intermediate gradient layer and a top roughness layer. But the growth interruptions result in an increase of the dense layer thickness and a decrease of surface roughness. The discrepancy of the refractive index measured by SE between bottom and upper layers can be reduced by growth interruptions or biasing the substrate. In the case of Vb=−50V, the film becomes well organized, the top surface appears smoother, and the refractive index can be increased greatly, without significant effect of growth interruptions.

Effect of growth interruption on the crystalline quality and electrical properties of Ga-doped ZnO thin film deposited on quartz substrate by magnetron sputtering

Ga-doped ZnO(GZO) thin films were deposited on the quartz substrate by magnetron sputtering system with growth interruption technique. As the number of interruptions and interruption time increased, the carrier concentration and Hall mobility in GZO films significantly increased. As a result, the resistivity of GZO films decreased. The optical transmittance of GZO films also increased with the number of interruption and interruption time. The transmittance showed over 90% in visual region. Atomic force microscopy measurement showed that the film surface became smoother with an increase of the number of interruption. In addition, the crystalline quality and electrical properties of GZO films were more improved when the growth interruption was employed with a temperature gradient.

InGaN/GaN heterostructures grown by submonolayer deposition

InGaN/(Al,Ga)N heterostructures containing ultrathin InGaN layers, grown by submonolayer deposition are studied. It is shown that significant phase separation with the formation of local In-enriched regions ∼3–4 nm in height and ∼5–8 nm in lateral size is observed in InGaN layers in the case of InGaN and GaN growth by cyclic deposition to effective thicknesses of less than one monolayer. The effect of growth interruption in a hydrogen-containing atmosphere during submonolayer growth on the structural and optical properties of InGaN/(Al,Ga)N heterostructures is studied. It is shown that these interruptions stimulate phase separation. It is also shown that the formation of In-enriched regions can be controlled by varying the effective InGaN and GaN thicknesses in the submonolayer deposition cycles.

Investigation of Wetting Layers in InAs/GaAs Self-Assembled Nanostructures with Reflectance Difference Spectroscopy

As a system with both profound physics and promising application potentials, the strain-induced self-assembled semiconductor nanostructures have been investigated for decades of years. The optical and electrical properties of this system are mainly determined by the nanostructures, but can be greatly affected by the generally existent two dimensional structures from which the nanostructures evolve, the so called wetting layer (WL). The WL configurations can be varied with different growth conditions, and further influence the nanostructure morphology and properties. This is a reviewing article introducing some recent progresses in investigating the evolution of WLs in InAs/GaAs system with reflectance difference spectroscopy. Different kinds of WL evolution processes in Stranski-Krastanov growth mode are introduced. The segregation and desorption of indium atoms and the effect of growth interruption are mentioned. The existence and the evolution process of wetting layers in droplet epitaxy method are also discussed.

Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

Effect of Growth Interruption in Migration Enhanced Epitaxy on InAs/GaAs Quantum Dots

In this study, we investigated the effect of growth interruption time (tGI) during migration enhanced epitaxy (MEE) growth of self-assembled InAs/GaAs quantum dots (QDs) to control the density of the QDs without any substrate rotation stop during QD formation. By manipulating the growth factor (tGI), the control of QD density in the range of 3.4 ×109–3.5 ×1010 dots/cm2, as well as the QD shape, was demonstrated. We concluded that three phenomena occur during growth interruption: 1) In re-evaporation, 2) In segregation, and 3) the redistribution of InAs QDs. From photoluminescence (PL), it is found that the emission wavelength of samples increased from 967.7 to 1151.7 nm as tGI increased due to redistribution. In addition, we confirmed PL peak emissions from QDs, quasi-three-dimensional (Q3D) clusters, and wetting layer. As a result, the manipulation of tGI in the MEE method can control the density, uniformity, size, and wavelength of QDs.

Investigation of the effect of growth interruption on the formation of InAs/GaAs quantum dot superlattice near the InAs critical thickness

Two kinds of superlattices (i) with and (ii) without growth interrupt (GI) after deposition of 1.77 monolayers (ML) of InAs on GaAs (0 0 1) were grown by solid-source molecular beam epitaxy (MBE) and assessed by transmission electron microscopy (TEM) techniques, double crystal X-ray diffraction (DCXRD) and photoluminescence (PL) measurements in order to gain an understanding of the structural and compositional properties. In case (i) formation of coherent dislocation free self-organized quantum dots (SOQDs) with 2.8–3.2 nm height and 13–16 nm lateral size was observed, whereas in case (ii) no quantum dots had formed. In order to better understand the implication of growth interruption for the formation mechanism, highly localised assessment of the composition of the QD was carried out via atomic resolution Z-contrast imaging and electron energy loss spectroscopy (EELS).

Photoluminescence and modulation spectroscopy study of the effects of growth interruptions on the interfaces of GaAsSb/GaAs multiple quantum wells

AbstractTemperature dependent photoluminescence (PL), room temperature phototransmittance (PT), contactless electroreflectance (CER) and wavelength modulated surface photovoltage spectroscopy (WMSPS) measurements are utilized to study the effects of growth interruption times, combined with Sb exposure of GaAsSb/GaAs multiple quantum wells (MQWs) structures. The PL spectra show peak location red‐shifted, luminescence intensity increased and full width at half maximum narrowed with increasing interruption time. The features originated from different regions of the samples including interband transitions of MQWs, interfaces and GaAs are observed and identified through a detailed comparison of the obtained spectra and theoretical calculation. The anomalous temperature dependence of PL spectra has been attributed to the carrier localization effect resulted from the presence of Sb clusters and/or fluctuations in Sb composition at the QW interfaces. An additional feature has also been observed below the GaAs region in Sb exposure treated samples and the probable origin of this feature has been discussed. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of growth interruption on the properties of InGaN/GaN MQWs grown by MOCVD

InGaN/GaN MQWs structures were grown by MOCVD. The effects of the growth interruption time on the optical and structural properties of InGaN/GaN MQWs were investigated. The experimental results show that the growth interruption can improve the interface quality, increase the intensity of photoluminescence (PL) and electroluminescence (EL); but if the interruption time was too long, the well thickness and the average In composition of MQWs decreased, and the EL intensity also decreased due to poor interface quality and impurities derived from growth interruption.

GaNAs/GaAs multiple quantum well grown by modulated N radical beam sequence of RF-MBE: Effect of growth interruption

GaNAs/GaAs multiple quantum wells (MQWs) were fabricated on GaAs (0 0 1) substrates by molecular beam epitaxy using N radical beam source. We have used modulated N radical beam source method in which N plasma is ignited only when the GaNAs layer is grown. We have investigated the effects of growth interruption (GI) after GaNAs layer growth on the MQW structure. High-resolution X-ray diffraction (HRXRD), transmission electron microscopy and low-temperature photoluminescence (PL) spectroscopy were used to study the N composition, structural and optical properties of the MQW structures. From results of the HRXRD and PL measurements, the drastic reduction and redistribution of N atoms in the GaNAs layers were found even by introduction of very short GI.

The effect of growth interruptions at the interfaces in epitaxially grown GaInAsSb/AlGaAsSb multiple-quantum-wells studied with high-resolution x-ray diffraction and photoluminescence

Molecular beam epitaxy has been used to grow GaInAsSb/AlGaAsSb multiple-quantum-well (MQW) structures. Growth has been interrupted at the interfaces between the wells and the barriers. During the growth interruptions, the interfaces have been exposed to Sbx(x=1, 2) and As2 fluxes. The structures have been studied using high-resolution x-ray diffraction (HRXRD) and photoluminescence (PL). The As content in the interface layers has been found to have a large impact on the HRXRD curves. The As content in the interface layers has been determined by simulation of HRXRD rocking curves. We also show how highly strained interfaces cause more satellite peaks to appear in HRXRD rocking curves. PL spectra show that interrupting growth at the interfaces between wells and barriers and exposing the interfaces to an Sb soak result in flatter interfaces.

Effect of growth interruption on optical properties of In-rich InGaN∕GaN single quantum well structures

In-rich InGaN∕GaN single quantum well (SQW) structures with and without growth interruption (GI) were successfully grown on sapphire substrates by metal-organic chemical vapor deposition. The optical properties were systematically investigated by photoluminescence (PL), selectively excited PL, PL excitation (PLE), and cathodoluminescence (CL) techniques. The integrated PL intensity of the main In-rich InGaN emissions for the sample grown without GI decreased only by a factor of 15.5 when the temperature increased from 11to300K, while that of the sample with GI decreased by about 1040, showing very good quantum efficiency for the sample without GI. The In-rich InGaN SQW emissions have been verified by selectively excited PL spectra and by the different PLE absorption edges. CL observations showed that the epilayer of the sample without GI agglomerated together to form clusters due to the large lattice and thermal mismatches with GaN, which confine the carriers in the clusters and ensure the relatively high quantum efficiency of the sample. The sample with GI showed relatively smooth surface with cluster structures jointed together, which gives two-dimensional QW environment in its energy band structure, and its optical emission is more sensitive to temperatures than that of the sample grown without GI.

Modulation spectroscopy study of the effects of growth interruptions on the interfaces ofGaAsSb/GaAs multiple quantum wells

The effects of growth interruption times combined with Sb exposure of GaAsSb/GaAsmultiple quantum wells (MQWs) have been investigated by using phototransmittance(PT), contactless electroreflectance (CER) and wavelength modulated surface photovoltagespectroscopy (WMSPS). The features originated from different portions of the samples,including interband transitions of MQWs, interfaces and GaAs, are observed and identifiedthrough a detailed comparison of the obtained spectra and theoretical calculation. Ared-shift of the interband transitions and a broader lineshape of the fundamentaltransition are observed from samples grown under Sb exposure compared to thereference sample grown without interruption. The results can be interpreted in termsof both increases in Sb content and mixing of Sb in the GaAs interface layers.An additional feature has been observed below the GaAs region in the sampleswith Sb treatment. The probable origin of this additional feature is discussed.

Influence of growth interruption on the formation of solid-state interfaces

In this study, the effects of growth interruptions on the formation of the interfaces in GaAs∕AlAs multilayers are investigated. For that purpose, a series of different samples has been manufactured with molecular-beam epitaxy. The introduction of growth interruptions of 50 s after the deposition of the layer leads to a change in the morphological properties of the interfaces, in particular their correlation length. These modifications due to the growth interrupt are analyzed with diffuse X-ray scattering. As a result of the measurements, an extension of the lateral correlation length can be proved. By contrast, the vertical correlation of the interfaces is not affected.