Effects of deposition rate on the size of self-assembled InP islands formed on GaInP/GaAs(100) surfaces

Utilizing the Stranski-Krastanov growth mode, three-dimensional InP islands are formed on a GalnP/GaAs surface using metalorganic chemical vapor deposition. The islands have been investigated with atomic force microscopy, and the effect of the deposition rate on the shape of the islands has been quantified. The height of the islands varies with deposition rate, whereas the basediameters are nearly constant around 1260 ± 35Å. The island height is 290 ± 12 Å at a high (2.6 ML/s) deposition rate and decreases to approximately 250 ± 16 Å for low (0.1 ML/ s) and moderate (0.8 ML/s) deposition rates.     

晶格畸变分析及其在半导体量子点结构中的应用

在适当的成像条件下可以直接从高分辨透射电子像（HRTEM）以接近原子级的分辨率进行晶格畸变分析。本综述介绍晶格畸变分析（LADIA）程序包及其在半导体自组装量子点（QD）系统中的应用。对多层InP小QD系统中畸变分布的分析表明：光致发光（PL）能量峰位的红移和QD中的应变弛豫直接相关。在慢速生长的InAs大QD系统中应变引起的元素互溶是PL峰位蓝移的主要因素。多层系统中QD的垂直叠合可解释为间隔层厚度低于临界值时生长前沿的横向张应变的作用。研究了生长以后不同条件快速退火对QD稳定性的影响，观测到垂直叠合的InPQD中出现各向异性的退火不稳定性。     

Self‐Assembled InAs Quantum Dots on InP(001) for Long‐Wavelength Laser Applications

Self‐assembled InAs quantum dots (QDs) embedded in an InAlGaAs matrix were grown on an InP (001) using a solid‐source molecular beam epitaxy and investigated using transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. TEM images indicated that the QD formation was strongly dependent on the growth behaviors of group III elements during the deposition of InAlGaAs barriers. We achieved a lasing operation of around 1.5 µm at room temperature from uncoated QD lasers based on the InAlGaAs‐InAlAs material system on the InP (001). The lasing wavelengths of the ridge‐waveguide QD lasers were also dependent upon the cavity lengths due mainly to the gain required for the lasing operation.     

Investigation of monolayer roughness in HgTe-CdTe superlattices

Infrared photoluminescence (PL) measurements were performed on (2ID-oriented superlattices with energy gaps in the range 110–495 meV. Most of the samples with thinner HgTe quantum wells displayed two PL peaks separated by Δhω ≈ 30–65 meV (which generally increased with decreasing well thickness). Both peak energies (E_p) sometimes varied gradually with location on the surface, and in one case three peaks of approximately equal spacing were observed in some locations. The data are consistent with a model which assumes the presence of randomly distributed islands having well thicknesses varying by approximately one monolayer. We find that Ahco and the variations of the spectra with temperature agree well with calculations based on this simple model.     

Properties of lnAsxP1-x layer formed by P-As exchange reaction on (001)lnP surface exposed to As4 beam

The P-As exchange reaction on InP surface exposed to As₄ beam was studied using photoluminescence (PL) and x-ray diffraction measurements as well as ultra-high vacuum scanning tunneling microscopy observation. It was found that as high as 90–95% of P can be exchanged by As and that the average depth of exchange reaction increases with the increase of As exposure time, being as deep as 5.5 ML for a long exposure. The splitting of PL peak takes place when the reaction depth exceeds 2 ML and the number of the split subpeaks increases with the increase of As exposure time. The PL peak splitting originates from the fluctuation of well thickness, caused by formation of InAs islands for strain relief during the exchange reaction.     

基于低温In_xGa_(1-x)P组分渐变缓冲层的InP/GaAs异质外延

采用低温GaAs与低温组分渐变InxGa1-xP作为缓冲层,利用低压金属有机化学气相外延(LP-MOCVD)技术,在GaAs(001)衬底上进行了InP/GaAs异质外延实验。实验中,InxGa1-xP缓冲层选用组分线性渐变生长模式(xIn0.49→1)。通过对InP/GaAs异质外延样品进行双晶X射线衍射(DCXRD)测试,并比较1.2μm厚InP外延层(004)晶面ω扫描及ω-2θ扫描的半高全宽(FWHM),确定了InxGa1-xP组分渐变缓冲层的最佳生长温度为450℃、渐变时间为500s。由透射电子显微镜(TEM)测试可知,InxGa1-xP组分渐变缓冲层的生长厚度约为250nm。在最佳生长条件下的InP/GaAs外延层中插入生长厚度为48nm的In0.53Ga0.47As,并对所得样品进行了室温光致发光(PL)谱测试,测试结果表明,中心波长为1643nm,FWHM为60meV。     

Metalorganic vapor phase epitaxial growth and structural characterization of GaAs/InP heterostructures

Highly mismatched GaAs epitaxial layers with thickness ranging from 15 nm to 7 μm have been grown on InP substrates by atomospheric pressure metalorganic vapor phase epitaxy. Layers thinner than 30 nm exhibited 3-D growth mechanism; in the thicker layers, the islands coalesced and then the growth followed the layer by layer mechanism. The elastic strain and the extended defects have been studied by high resolution x-ray diffraction and transmission electron microscopy, respectively. The common observation of planar defects, misfit, and threading dislocations in the layers has been confirmed. The results on the elastic strain release have been discussed on the basis of the equilibrium theory.     

Growth and photoluminescence study of ZnSe quantum dots

We report detailed photoluminescence (PL) studies of ZnSe quantum dots grown by controlling the flow duration of the precursors in a metal-organic chemical vapor deposition system. The growth time of the quantum dots determines the amount of blue shift observed in the PL measurements. Blue shift as large as 320 meV was observed, and the emission was found to persist up to room temperature. It is found that changing the flow rate and the total number of quantum dot layers also affect the peak PL energy. The temperature dependence of the peak PL energy follows the Varshni relation. From analyzing the temperature-dependent integrated intensity of the photoluminescence spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of the exciton in ZnSe quantum dot.     

Optical characterisation of Ge islands grown on Si(110)

The growth of Ge islands on Si(110) substrates by low pressure chemical vapour deposition has been studied. Atomic force microscopy images reveal that multifaceted dome shaped islands appear on samples where the two-dimensional (2D) to three-dimensional (3D) growth mode changeover has occurred. Photoluminescence (PL) spectroscopy was used to investigate the growth as a function of the Ge coverage. The excitation power dependence of island PL spectra allowed one to point out a band filling effect and to determine the efficiency of radiative recombinations. In addition, island PL peak evolution with temperature underlined a good hole confinement.     

Electrical characterization of high purity InGaAsP alloys

In_xGa_1-xAs_yP_1-y layers grown by liquid phase epitaxy on InP substrates were characterized by Hall effect between 4 and 300K. The thermal activation energy of donor impurities was estimated from the temperature dependence of the free electron concentration ; it was found to increase with phosphorus concentration from less than 1meV in InGaAs to about 2.5meV in InP. Evidence for impurity conduction was also observed in some samples at the lowest temperatures. The mobility analysis led to an estimation of the alloy scattering potential in the whole range of compositions 0≤y≤l. At temperatures below 10K, we observed avalanche effect due to impact ionization of electrons from shallow donor impurities into the conduction band.     

Modified fermi-level pinning of the (100) GaAs surface through InAs quantum dots in different stages of overgrowth

The presence of InAs quantum dots on a {100} GaAs surface results in a pronounced increase of the Fermi level pinning energy. Using room-temperature photo-reflectance measurements combined with atomic force microscopy, we find that the presence of the quantum dots results in the Fermi level being pinned approximately ∼250 meV deeper in the bandgap, an effect which is reversed by either removing or overgrowing the dots. Both overgrowth and complete etching of quantum dots results in the disappearance of the polar InAs facets; we explain the change in Fermi level in terms of such facets. We also discuss the phase delay for the InAs related feature of the photoreflectance experiment as a detrapping of photo-generated electron-hole pairs in the dots.     

LP-MOCVD grown (lnAs)m(GaAs)m short period superlattices on InP

(InAs)_m(GaAs)_m (1 ≤ m ≤ 12) short period superlattices (SPSs) have been grown on semi-insulated InP substrates with a 200 nm InP cap layer using low pressure metalorganic chemical vapor deposition (MOCVD). According to double crystal x-ray diffraction and transmission electron microscopy results, the critical layer thickness of (InAs)_m(GaAs)_m SPS was observed to be ～30Å (m = 5). For the SPS below the critical layer thickness, mirror-like surface morphology was found without defects, and strong intensity Fourier transformed photoluminescence (FT-PL) spectra were also obtained at room temperature. The SPS with m = 4 showed a drastic improvement in photoluminescence intensity of order of two compared to an InGaAs ternary layer. However, the SPS with a large value of m (m ≥ 6), rough surface was observed with defects, with broad and weak FT-PL spectra. The surface morphology of SPS was greatly affected by the substrate orientation. The SPS with m = 5 was grown on two degree tilted substrate from (100) direction and showed poor surface morphology as compared to the one grown on (100) exact substrate Moreover, the SPS grown on a (111)B substrate showed a rough triangular pattern with Nomarski optical microscopy. In-situ thermal annealed SPS with m = 4 showed a 18 meV increase in PL peak energy compared to the as-grown sample due to phase separation resulting from thermal interdiffusion.     

Structural and optical properties of GaxIn1−xP layers grown by chemical beam epitaxy

Chemical beam epitaxial (CBE) Ga_xIn_1?xP layers (x≈0.5) grown on (001) GaAs substrates at temperatures ranging from 490 to 580°C have been investigated using transmission electron diffraction (TED), transmission electron microscopy, and photoluminescence (PL). TED examination revealed the presence of diffuse scattering 1/2{111}_B positions, indicating the occurrence of typical CuPt-type ordering in the GaInP CBE layers. As the growth temperature decreased from 580 to 490°C, maxima in the intensity of the diffuse scattering moved from ½{111}_B to ½{?1+δ,1?δ,0} positions, where δ is a positive value. As the growth temperature increased from 490 to 550°C, the maxima in the diffuse scattering intensity progressively approached positions of $\frac{1}{2}\{\bar 110\} $ , i.e., the value of δ decreased from 0.25 to 0.17. Bandgap reduction (～45 meV) was observed in the CBE GaInP layers and was attributed to the presence of ordered structures.     

Effects of growth interruption on the evolution of InAs/InP self-assembled quantum dots

We investigated the change in the structural and optical properties of InAs/InP quantum structures during growth interruption (GI) for various times and under various atmospheres in metalorganic chemical vapor deposition. Under AsH₃ + H₂ atmosphere, the mass transport for the 2D-to-3D transition was observed during the GI. Photoluminescence peaks from both quantum dots (QDs) and quantum wells were observed from the premature QD samples. The fully developed QDs showed the two distinct temperature regimes in the PL peak position, full width at half maximum (FWHM) and wavelength-integrated peak intensity. The two characteristic activation energies were obtained from the InAs/InP QDs: ∼10 meV for intra-dot excitation and 90 ∼ 110 meV for the excitation out of the dots, respectively. It was also observed that the QD evolution kinetics could be suppressed in PH₃ + H₂ and H₂ atmospheres. The proper control of GI time and atmosphere might be a useful tool to further improve the properties of QDs.     

Optical and crystallographic properties of high perfection InP grown on Si(111)

The growth of InP by low-pressure metalorganic chemical vapor deposition on vicinal Si(111), misoriented 3° toward [1-10], is reported. Antiphase domain-free InP is obtained without any preannealing of the Si substrate. Crystallographic, optical, and electrical properties of the layers are significantly improved as compared to the best reported InP grown on Si(001). The high structural perfection is demonstrated by a full width at half maximum (FWHM) of 121 arcs for the (111) Bragg reflex of InP (thickness = 3.4 μm) as obtained by double crystal x-ray diffraction. The low-temperature photoluminescence (PL) efficiency is 70% of that of homoepitaxially grown InP layers. The FWHM of the near-gap PL peak is only 2.7 meV as compared to 4.5 meV of the best material grown on Si(001). For the first time, InP:Fe layers with semi-insulating characteristics (ρ > 3 × 10⁷ Ω-cm) have been grown by compensating the low residual background doping using ferrocene. Semi-insulating layers are prerequisite for any device application at ultrahigh frequencies.     

Photoluminescence analysis of InAIAs-InGaAs HFET Material with Varied Placement of Heavy δ-Doping

Low temperature photoluminescence (PL) has been used to characterize InAlAs/InGaAs/InP heterojunction field-effect transistor (HFET) structure material. A phenomenological lineshape model has been applied to the PL spectrum to derive energy levels and the position of the Fermi-energy and hence the channel carrier concentration. The data is compared with results from low-temperature Hall and Shubnikov-de Hans (SdH) measurements, and fit with a charge-control model of the conduction band. Values for the sheet density are derived from PL for channel-doped structures where SdH measurements are difficult. Changes in the quantum well symmetry through variations in the dopant distribution are shown to be reflected in the PL lineshape.     

Optical and photocatalytic properties of indium phosphide nanoneedles and nanotubes

Large scale indium phosphide (InP) nanoneedles and nanotubes were synthesized through a facile solvothermal reaction. The morphology and microstructure of the samples were analyzed by employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and Ultraviolet-visible (UV–vis) spectroscopy. The room temperature photoluminescence (PL) measurements showed that the InP nanoneedles and nanotubes possessed a pronounced blue shift in contrast to the bulk counterpart, which was ascribed to the crystalline defects effect. Moreover, the InP nanotubes exhibited an enhanced photocatalytic performance as compared to the InP nanoneedles and nanoparticles.     

Investigations on indium phosphide grown by chemical beam epitaxy

In this paper, we present a systematic study of the properties of indium phosphide (InP) layers grown by chemical beam epitaxy (CBE). Trimethylindium (TMIn) and phosphine (PH₃) are used as source materials. The relation between the phosphine cracker temperature and the cracking efficiency has been studied by mass spectroscopy during growth. The growth rate and morphology of the layers have been studied by varying the TMIn and phosphine flow rates as well as the substrate temperature. We have found that, under a wide range of growth conditions, the deposition rate is only determined by and proportional to the TMIn flow rate. This is in agreement with literature. Additionally, we observe that the growth rate decreases below a certain phosphine to TMIn flow rate (V/III) ratio and becomes phosphine flow limited. From investigations of the growth rate as a function of temperature, it is concluded that the desorption of indium species from InP starts at a temperature slightly below 540°C. For this desorption process, we have found an activation energy of (217 ± 20) kJ/mol. Further characterization of the InP layers has been carried out by photoluminescence and Hall measurements. From both methods, the optimum growth conditions have been established. Under these conditions, we reproduc-ibly obtain InP layers showing linewidths of the donor-bound exciton transition at 5K around 0.25 meV and a mobility at 77K of about 7.0·10⁴ cm²/Vs. From the analysis of the mobility in the temperature range from 20 to 300K, we conclude that, additionally to shallow donors and acceptors, deep-donor centers with an activation energy of about 150 meV are present in all layers.     

Molecular beam epitaxial growth of MgZnCdSe on (100) InP substrates

Wide-gap II-VI MgZnCdSe quaternary compounds were grown on InP substrates by molecular beam epitaxy, for the first time. Changing the Mg composition (x = 0 to 0.63), various Mg_x(Zn_yCd_{1_y})_{1_x}Se lattice-matched to InP were grown. Mirror-like surface morphologies and streaky reflection high energy electron diffraction patterns of MgZnCdSe were obtained. With increased Mg compositions, the band-edge emissions wavelength in photoluminescence spectra was shifted from 572 nm (2.17 eV) to 398 nm (3.12 eV) at 15K. Furthermore, the absolute PL peak intensity increased drastically with increased band-edge emission, being accompanied by a relative decrement in the deep level emission intensities were also observed.     

Atomic structures of Au and Ag films epitaxially grown on the InP(001)-p(2 × 4) surface

Thin films of Au and Ag deposited onto the InP(001)-p(2 × 4) surface at room temperature have been characterized by means of combined surface-layer analysis of low energy electron diffraction, reflection high energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spec-troscopy-channeling techniques. It has been found that the Au film grows epitaxially in the layer-by-layer mode along the <001> direction, while the Ag film grows in the <110> direction in the Stranski-Krastanov mode. The unit cell of a face-centered cubic lattice of the Au film is rotated azimuthally by 45° with respect to the unit cell of a zinc-blende lattice of the InP substrate. The islands of Ag(110) crystallites prefer to orient their (100) faces along the direction of the 4 times superlattice of the InP(001)-p(2 × 4) surface. The analysis of the RBS-channeling minimum yield of 1.5 MeVHe⁺ ions incident along the [001] direction of the InP(OOl) substrate shows that both the epitaxially grown Au film and Ag crystallite of less than 20Å in thickness are excellent in crystalline quality.