Structural and optical characterization of InAs nanostructures grown on high-index InP substrates

The structural and optical properties of InAs layers grown on high-index InP surfaces by molecular beam epitaxy are investigated in order to understand the self-organization of quantum dots and quantum wires on novel index surfaces. Four different InP substrate orientations have been examined, namely, (1 1 1)B, (3 1 1)A, and (3 1 1)B and (1 0 0). A rich variety of InAs nanostructures is formed on the surfaces. Quantum wire-like morphology is observed on the (1 0 0) surface, and evident island formation is found on (1 1 1)A and (3 1 1)B by atomic force microscopy. The photoluminescence spectra of InP (1 1 1)A and (3 1 1)B samples show typical QD features with PL peaks in the wavelength range 1.3-1.55 mu m with comparable efficiency. These results suggest that the high-index substrates are promising candidates for production of high-quality self-organized QD materials for device applications. (C) 1999 Elsevier Science B.V. All rights reserved.

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8-12 mu m infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers. (C) 1999 Elsevier Science B.V. All rights reserved.

Substrate surface atomic structure influence on the growth of InAlAs quantum dots

We have examined the influence of substrate surface orientation on self-assembled InAlAs/AlGaAs quantum dots grown on (0 0 1) and (n 1 1) A/B (n = 3, 5) GaAs substrates by molecular beam epitaxy (MBE). Preliminary characterizations have been performed using photoluminescence (PL) and transmission electron microscopy (TEM). The PL emission energies of quantum dots on high Miller index surface are found to be strongly dependent on the atomic-terminated surface (A or B surface) of the substrate. We observed that there were planar ordering larger islands on (3 1 1)B surface compared to (0 0 1) surface, in contrast, a rough interface and smaller "grains" on (3 1 1)A surface, this result is identical with PL emission energy from these islands. We propose that the rapid strain-induced surface "roughening" impedes the formation of 3D islands on A surface, and indicating that this is a promising approach of the realization of ordering distribution on (3 1 1)B plane for devices such as red-emitting semiconductor quantum dots lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

Cubic-phase GaN light-emitting diodes

The feasibility of growing device-quality cubic GaN/GaAs(001) films by metal organic chemical vapor deposition has been demonstrated. The optical quality of the GaN films was characterized by room-temperature photoluminescence measurements, which shows a full width at half maximum of 46 meV. The structural quality of the films was investigated by transmission electron microscopy. There are submicron-size grains free from threading dislocations and stacking faults. More importantly, a cubic-phase GaN blue light-emitting diode has been fabricated. The device process, which is very simple and compatible with current GaAs technology, indicates a promising future for the blue light-emitting diode. (C) 1999 American Institute of Physics. [S0003-6951(99)01416-3].

Cubic InGaN grown by MOCVD

We report on the growth of high-quality cubic phase InGaN on GaAs by MOCVD. The cubic InGaN layers are grown on cubic GaN buffer layers on GaAs (001) substrates. The surface morphology of the films are mirror-like. The cubic nature of the InGaN films is obtained by Xray diffraction (XRD) measurements. The InGaN layers show strong photoluminescence (PL) at room temperature. Neither emission peak from wurtzite GaN nor yellow luminescence is observed in our films. The highest In content as determined by XRD is about 17% with an PL emission wavelength of 450 nm. The FWHM of the cubic InGaN PL peak are 153 meV and 216 meV for 427 nm and 450 nm emissions, respectively. It is found that the In compositions determined from XRD are not in agreement with those estimated from PL measurements. The reasons for this disagreement are discussed.

Photoluminescence properties of nitrogen-doped ZnSe epilayers

The photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown on semi-insulating GaAs(100) substrates by MBE using a rf-plasma source for N doping were investigated. The PL peak which can be related to N acceptor was observed in the PL spectra of ZnSe:N smaples. At 10K, as the excitation power density increases, the energy of donor-acceptor pair(DAP) emission shows a blue-shift and its intensity tends to saturate. As the temperature increases over a range from 10K to 300K, the relative PL intensity of donor bound exciton to that of the acceptor bound exciton increases due to the transfer between two bound excitons.

Size quantization effects in InAs self-assembled islands on InP(001) at the onset of 2D-to-3D transition

Photoluminescence spectroscopy has been used to investigate self-assembled InAs islands in InAlAs grown on InP(0 0 1) by molecular beam epitaxy, in correlation with transmission electron microscopy. The nominal deposition of 3.6 monolayers of InAs at 470 degrees C achieves the onset stage of coherent island formation. In addition to one strong emission around 0.74 eV, the sample displaces several emission peaks at 0.87, 0.92. 0.98, and 1.04 eV. Fully developed islands that coexist with semi-finished disk islands account for the multipeak emission. These results provide strong evidence of size quantization effects in InAs islands. (C) 1999 Elsevier Science B.V. All rights reserved.

In composition dependence of lateral ordering in InGaAs quantum dots grown on (311)B GaAs substrates

Self-assembled InxGa1-xAs quantum dots (QDs) on (311)A/B GaAs surfaces have been grown by molecular beam epitaxy (MBE). Spontaneously ordering alignment of InxGa1-xAs with lower In content around 0.3 have been observed. The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the (311)B surface, and is strongly dependent upon the In content x. The ordering alignment become significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on (100) or (311)A substrates. (C) 1999 Elsevier Science B.V. All rights reserved.

InAs/ln(0.52)Al(0.48)As quantum wire structure with the specific layer-ordering orientation on InP(001)

Quantum wires were formed in the 6-period InAs/In0.52Al0.48As structure on InP(0 0 1) grown by molecular beam epitaxy. The structure was characterized with transmission electron microscopy. It was found that the lateral periodic compositional modulation in the QWR array was in the [1 (1) over bar 0] direction and layer-ordered along the specific orientation deviating from the [0 0 1] growth direction by about 30 degrees. This deviating angle is consistent with the calculation of the distribution of elastic distortion around quantum wires in the structure using the finite element technique. (C) 1999 Elsevier Science B.V. All rights reserved.

Uniformity enhancement of the self-organized InAs quantum dots

Growth interruption was introduced after the deposition of GaAs cap layer, which is thinner than the height of quantum dots. Uniformity of quantum dots has been enhanced because the full-width of half-maximum of photoluminescence decrease from 80 to 27 meV in these samples as the interruption time is increased. Meanwhile, we have observed that the peak position of photoluminescence is a function of interruption time, which can be used to modulate energy level of quantum dots. All of the phenomenon mentioned above can be attributed to the diffusion of In atoms from the tops of InAs islands to the top of GaAs cap layer caused by the difference between the surface energies of InAs and GaAs. (C) 1999 Elsevier Science B.V. All rights reserved.

Quantitative analysis of excitonic photoluminescence in nitrogen-doped ZnSe epilayers

We have investigated the photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen radio frequency-plasma source. The PL data shows that the relative intensity of the donor-bound exciton (I-2) emission to the acceptor-bound exciton (I-1) emission strongly depends on both the excitation power and the temperature. This result is explained by a thermalization model of the bound exciton which involved in the capture and emission between the neutral donor bound exciton, the neutral acceptor bound exciton and the free exciton. Quantitative analysis with the proposed mechanism is in good agreement with the experimental data. (C) 1999 American Institute of Physics. [S0021-8979(99)09102-1].

Self-limiting MBE growth and characterization of three-dimensionally confined nanostructures on patterned GaAs(311)A substrates

The formation of triangular-shaped dot-like (TD) structures grown by molecular beam epitaxy on GaAs (311)A substrates patterned with square- and triangular-shaped holes is compared. On substrates patterned with square-shaped holes, TD structures are formed via the pinch-off of two symmetrically arranged {111} planes which develop freely in the regions between the holes on the original substrate surface, while the (111)A sidewalls of the as-etched holes develop a rough morphology during growth. The evolution of the rough ( 1 1 1)A sidewalls is eliminated on substrates patterned with triangular shaped holes resulting in similar TD structures with highly improved uniformity over the entire pattern. Spectrally and spatially resolved cathodoluminescence spectroscopy reveals the lateral variation of the quantum-well confinement energy in the TD structures generating distinct lateral energy barriers between the top portion and the nearby smooth regions with efficient radiative recombination. Formation of TD structures provides a new approach Do fabricate three-dimensionally confined nanostructures in a controlled manner.

Photoluminescence properties of SiGe/Si single wells with fluctuating structural parameters

Photoluminescence properties of SiGe/Si single wells with fluctuating structural parameters are studied. Four SiGe/Si single wells have been grown on Si(001) at 750 degrees C by disilane and solid Ge molecular beam epitaxy with varied disilane cracking-temperatures. Intense NP and TO-phonon replicas are detected up to 70 K in the photoluminescence spectra and the activation energy of the thermal quenching of the photoluminescence is 28 +/- 4 meV. The high growth temperature and purposeful introduction of fluctuation of structural parameters may be responsible for the improvement of the thermal quenching property.

Metamorphosis of self-organized quantum dots into quantum wires

Spontaneous formation of InAs quantum wires in InAlAs on InP(001) via sequential chain-like coalescence of quantum dots along [1 (1) over bar 0] is realized. Theoretical calculations based on the energetics of interacting steps provide a qualitative explanation for the experimental results. Sequential coalescence of initially isolated dots reduces the total free energy strikingly. Thus the wire-like structure is energetically favorable. (C) 1998 Elsevier Science B.V.

Structure and photoluminescence of InGaAs self-assembled quantum dots grown on InP(001)

Molecular beam epitaxy has been used for growing InGaAs self-assembled quantum dots (QDs) in InAlAs on an InP(001) substrate. Nominal deposition of 9.6 monolayers of In0.9Ga0.1As results in QDs of similar to 6.5 nm high with an areal density of 3.3 X 10(11) cm(-2). Conspicuous bimodal size distribution is identified, and is responsible for the observed QDs photoluminescence (PL) emission with two peaks at 0.627 and 0.657 eV. Good agreement is achieved between the observed PL peak energies and calculated results. (C) 1999 American Institute of Physics. [S00218979(99)00101-2].