Zhi Jin

Self-organized InAs quantum dots formation by As/P exchange reaction on (001) InP substrate

In this letter, we present the results of InAs quantum dots (QDs) prepared on a (001) InP substrate. As/P exchange reaction at the surface of InP buffer was used to form the InAs islands in the reactor of low pressure metalorganic chemical vapor deposition at 600 °C. Preliminary characterizations of the InAs QDs have been investigated by using atomic force microscopy and photoluminescence (PL). Room temperature PL emission from the 0-dimensional system centers at 1520 nm and the full width at half maximum of the PL is 92 meV.

Using the tensile stress field to control quantum dot arrangements

In this paper, a tensile-strained layer is used to control the quantum dot arrangements. A 3 nm GaAs tensile-strained layer is grown on InP (001) substrate, and a four-monolayer InAs compressed layer is then grown on top by LP-MOVPE. Atomic force microscopy (AFM) measurements were performed. AFM images indicate that the InAs quantum dots are arranged along two orthogonal directions, their diameter is about 30 nm, the size fluctuation is only 10%, and their density is 8.8×109 cm−2, which is higher than that grown directly on InP or GaAs substrates. An identical structure, except for the presence of 30 nm of GaAs, was also grown. The islands on top of the 30 nm GaAs are mainly very big and rectangular in shape. We demonstrate that these characteristics originate from the modulated stress field of the GaAs tensile-strained layer.

Characteristics of InAs quantum dots on GaAs/InP with different InAs coverage

In this article, a thin tensile GaAs interlayer was used to get narrower size distribution and regular arrangement of InAs quantum dots (QDs) on InP substrate by low-pressure metalorganic chemical vapor deposition. The comparison results of the photoluminescence spectrum and the atomic force microscopy image show better properties after using GaAs interlayer. Also investigated were the surface behaviors of InAs QDs with different InAs coverage on GaAs/InP in order to reveal the detailed information of InAs QDs.

Photoluminescence of InAs Self-Organized Quantum Dots Formation on InP Substrate by MOCVD

In this letter, we present results of photoluminescence (PL) emission from single-layer and multilayer InAs self-organized quantum dots (QDs), which were grown on (001) InP substrate. The room temperature PL peak of the single-layer QDs locates at 1608 nm, and full width at half-maximum (FWHM) of the PL peak is 71 meV. The PL peak of the multilayer QDs locates at 1478 nm, PL intensity of which is stronger than that of single-layer QDs. The single-layer QD PL spectra also display excited state emission and state filling as the excitation intensity is increased. Low temperature PL spectra show a weak peak between the peaks of QDs and wetting layer (WL), which suggests the recombination between electrons in the WL and holes in the dots.

Effect of thin GaAs tensile-strained layer on InAs quantum dots on InP (001) substrate grown by LP-MOVPE

Abstract The InAs quantum dots on thin tensile-strained GaAs layer on InP (001) substrate are grown by LP-MOVPE. Approximately 2 nm GaAs tensile-strained layer is first grown on InP substrate, then 2 monolayer (ML) InAs for sample A, 4 ML for sample B, 6 ML for sample C and 8 ML for sample D are deposited. An atomic force microscope (AFM) is used to study the behavior of the InAs quantum dots. For sample A, two types of InAs islands are observed. Strain-induced grooves appear on the surface. For the other three samples, the InAs islands arrange along two orthogonal directions and the island density decreases with an increase in the amount of InAs material. The density of sample B is as high as 1.9×10 10 cm −2 , the densities are 1.39×10 10 and 0 .79×10 10 cm −2 for samples C and D, respectively. Furthermore, the base shape changes for different samples. For samples A and B, the base shapes are round; for sample C, the base changes into ellipsis; but for sample D, the base changes into triangle. The base area increases with an increase in the deposition of InAs. We also investigate the PL spectrum of InAs QDs with GaAs and with it and find that the QDs quality is higher with GaAs layer.

Effects of misfit dislocation interaction and 90°-type misfit dislocations on strain relaxation behavior in strained epilayer

Abstract The effects of misfit dislocation interaction and 90°-type misfit dislocations on strain relaxation behavior in a strained layer are considered theoretically. Our results show that the interaction of misfit dislocations is responsible for the large residual strain in the strained epilayer and that 90°-type misfit dislocations play a very important role in the final stage of strain relaxation. The strain is relaxed more completely by 90° misfit dislocations than by 60° dislocations. The theory is consistent with experimental results.

Influence of the amount of InAs on InAs quantum dots on thin GaAs tensile-strained layer on [001] InP substrate

We study the behavior of InAs QDs on thin tensile-strained GaAs layer with different amount of InAs. The samples are grown by LP-MOCVD using TMIn, TMGa, pure AsH/sub 3/ and 10% PH/sub 3/ as precursors. The InP buffer layer is grown at 600 /spl deg/C after the thermal etching, which is performed at 650 /spl deg/C under the protection of PH/sub 3/. Then about 3 nm GaAs tensile-strained layers are grown at 500 /spl deg/C. Finally, 2ML InAs for S/sub 1/, 4ML for S/sub 2/, 6ML for S/sub 3/, and 8ML for S/sub 4/, are deposited at the growth rate of 0.3 ML/s. We use AFM to study the surface morphology of samples.

A new expression of excess stress and the stability of buried strained heterostructures

Abstract A new mechanism of strain relaxation in buried strained layers is proposed. According to this mechanism, the mixture of single and paired misfit dislocations appears to relax the misfit strain. The corresponding formula of excess force and stresses is derived. In this formula, the free-surface boundary condition, the interaction and distribution of misfit dislocations are all incorporated. The formula can be applied to arbitrary strained heterostructures. Both single- and double-kink models are some extreme condition of our formula. A formula of the critical thickness of the strained layer is derived.

EFFECT OF NON-STRAINED CAPPING LAYER ON EXCESS STRESS IN STRAINED LAYERS

The effects of the capping-layer thickness and the discrepancy of the numbers of misfit dislocations at the upper and lower interfaces in capped layer on the excess stress are considered. Based on this, the formulae of excess stresses for single-and double-kink models are modified and a new formula is derived, which unifies single- and doublekink models and is valid for arbitrary capping-layer thickness. It is useful to complete the description of the formation and motion of misfit dislocations in strained layers.

The effects of misfit dislocation distribution and capping layer on excess stress

It is generally accepted that in the buried strained-layer structure, the strain is relaxed by paired misfit dislocations: one at the upper interface and the other at the lower interface. But, experimentally it is not so. In this letter, the effect of a mixture of single and paired misfit dislocations is incorporated in the formula of excess force. In this formula, the effects of the capping layer with arbitrary thickness and the interaction of misfit dislocations at different interfaces are also included. Based on the formula, the excess stresses are derived. These formulas can be used to predict the excess stress of strained layers with arbitrary heterostructure structures. They also can describe the transition process from the single-kink to the double-kink mechanism.