Observation of deep electron states in n-type Al-doped ZnS1-xTex grown by molecular beam epitaxy

Deep level transient spectroscopy (DLTS) technique was used to investigate deep electron states in n-type Al-doped ZnS1-xTex epilayers grown by molecular fiction epitaxy (MBE), Deep level transient Fourier spectroscopy (DLTFS) spectra of the Al-doped ZnS1-xTex (x = 0. 0.017, 0.04 and 0.046. respectively) epilayers reveal that At doping leads to the formation of two electron traps at 0.21 and 0.39 eV below the conduction hand. 1)DLTFS results suggest that in addition to the rules of Te as a component of [lie alloy as well as isoelectronic centers, Te is also involved in the formation of all electron trip, whose energy level relative to the conduction hand decreases a, Te composition increases.

GaInNAs/GaAs quantum well lasers grown by solid-source molecular beam epitaxy

The growth of GaInNAs/GaAs quantum wells (QW) was investigated by solid-source molecular beam epitaxy. N was introduced by a dc-active plasma source. The effect of growth conditions such as on the N incorporation and photoluminescence (PL) intensity of the QWs has been studied. The PL peak intensity decreased and the PL fun width at half maximum increased with increasing N concentrations. The highest N concentration of 2.6% in a GaInNAs/GaAs QW was obtained, and corresponding to a PL peak wavelength of 1.57 mum at 10K. Rapid thermal annealing at 850degreesC significantly improved the crystal quality of the QWs. An optimum annealing time of 5s at 850degreesC was obtained. A GaInNAs/GaAs SQW laser with the emitting wavelength of 1.2 mum and a high characteristic temperature of 115 K was achieved at room temperature.

Photoluminescence characterization of 1.3 mu m In(Ga)As/GaAs islands grown by molecular beam epitaxy

1.3 mum wavelength In(Ga)As/GaAs nanometer scale islands grown by molecular beam epitaxy (MBE) were characterized by photoluminescence (PL) and atomic force microscopy (AFM) measurements. It is shown that inhomogeneous broadening of optical emission due to fluctuation of the In0.5Ga0.5As islands both in size and in compositions can be effectively suppressed by introducing a AlAs layer and a strain reduction In0.2Ga0.8As layer overgrown on top of the islands, 1.3mum emission wavelength with narrower line-width less than 20meV at room temperature was obtained.

Room-temperature continuous-wave lasing from InAs GaAs quantum dot laser grown by molecular beam epitaxy

Quantum dot lasers are predicted to have proved lasing characteristics compared to quantum well and quantum wire lasers. We report on quantum dot lasers with active media of vertically stacked InAs quantum dots layers grown by molecular beam epitaxy. The laser diodes were fabricated and the threshold current density of 220 A/cm(2) was achieved at room temperature with lasing wavelength of 951 nm. The characteristic temperature To was measured to be 333K and 157K for the temperature range of 40-180K and 180-300K, respectively.

Current-induced migration of surface adatoms during GaN growth by molecular beam epitaxy

The influence of electric fields on surface migration of Gallium (Ga) and Nitrogen (N) adatoms is studied during GaN growth by molecular beam epitaxy (MBE). When a direct current (DC) is used to heat the sample, long distance migration of Ga adatoms and diffusion asymmetry of N adatoms at steps are observed. On the other hand, if an alternating current (AC) is used, no such preferential adatom migration is found. This effect is attributed to the effective positive charges of surface adatoms. representing an effect of electro-migration. The implications of such current-induced surface migration to GaN epitaxy are subsequently investigated. It is seen to firstly change the distribution of Ga adatoms on a growing surface, and thus make the growth to be Ga-limited at one side of the sample but N-limited at the other side. This leads to different optical qualities of the film and different morphologies of the surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Growth and characterization of GaInNAs/GaAs by plasma-assisted molecular beam epitaxy

We have studied the growth of GaInNAs/GaAs quantum well (QW) by molecular beam epitaxy using a DC plasma as the N sourer. The N concentration was independent of the As pressure and the In concentration, but inversely proportional to the growth rate. It was almost independent of T, over the range of 400-500 degreesC, but dropped rapidly when T-g exceeded 500 degreesC. Thermally-activated N surface segregation is considered to account for the strong falloff of the N concentration. As increasing N concentration, the steep absorption edge of the photovoltage spectra of GaInNAs/GaAs QW became gentle, the full-width at half-maximum of the photoluminescence (PL) peal; increased rapidly, and a so-called S-shaped temperature dependence of PL peak energy showed up. All these were attributed to the increasing localized state as N concentration. Ion-induced damage was one of the origins of the localized state. A rapid thermal annealing procedure could effectively remote the localized state. (C) 2001 Elsevier Science D.V. All rights reserved.

Quality improvement of GaInNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The optimum growth condition of GaInNAs/GaAs quantum wells (QWs) by plasma-assisted molecular beam epitaxy was investigated. High-resolution X-ray diffraction and photoluminescence (PL) measurements showed that ion damage drastically degraded the quality of GaNAs and GaInNAs QWs and that ion removal magnets can effectively remove the excess ion damage. Remarkable improvement of PL intensity and obvious appearance of pendellosung fringes were observed by removing the N ions produced in the plasma cell. When the growth rate increased from 0.73 to 1.2 ML/s, the optimum growth temperature was raised from 460 degreesC to 480 degreesC and PL peak intensity increased two times. Although the N composition decreased with increasing growth rate, degradation of optical properties of GaInNAs QWs was observed when the growth rate was over 0.92 ML/s. Due to low-temperature growth of GaInNAs QWs, a distinctive reflection high-energy electron diffraction pattern was observed only when the GaAs barrier was grown under lower As-4 pressure. The samples with GaAs barriers grown under lower As-4 pressure (V/III ratio about 24) exhibited seven times increase in PL peak intensity compared with those grown under higher As-4 pressure (V/III ratio about 50). (C) 2001 Elsevier Science B,V. All rights reserved.

Influence of substrate orientation on In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

In this paper, In0.5Ga0.5As quantum dots are fabricated on GaAs (100) and (n11)A/B (n = 3, 5) substrates by molecular beam epitaxy. Atomic force microscopy shows that the quantum dots on each oriented substrate are different in size, shape and distribution. In addition, photoluminescence spectra from these quantum dots are different in emission peak position, line width and integrated intensity. Auger electron spectra demonstrate that In concentration is larger near the surface than inside quantum dots, suggesting the occurrence of surface segregation effect during the growth of InGaAs dots. The surface segregation effect is found to be related to substrate orientation. (C) 2000 Elsevier Science B.V. All rights reserved.

Electrical properties of GaN deposited on nitridated sapphire by molecular beam epitaxy using NH3 cracked on the growing surface

We have found that GaN epilayers grown by NH3-source molecular beam epitaxy (MBE) contain hydrogen. Dependent on the hydrogen concentration, GaN on (0001) sapphire can be either under biaxially compressive strain or under biaxially tensile strain. Furthermore, we notice that background electrons in GaN increase with hydrogen incorporation. X-ray photoelectron spectroscopy (XPS) measurements of the N1s region indicate that hydrogen is bound to nitrogen. So, the microdefect Ga...H-N is an effective nitrogen vacancy in GaN, and it may be a donor partly answering for the background electrons. (C) 1999 Elsevier Science B.V. All rights reserved.

Gas source molecular beam epitaxy and thermal stability of Si1-xGex/Si superlattice materials

Gas source molecular beam epitaxy has been used to grow Si1-xGex alloys and Si1-xGex/Si multi-quantum wells (MQWs) on (100) Si substrates with Si2H6 and GeH4 as sources. Heterostructures and MQWs with mirror-like surface morphology, good crystalline qualify, and abrupt interfaces have been studied by a variety of in situ and ex situ techniques. The structural stability and strain relaxation in Si1-xGex/Si heterostructures have been investigated, and compared to that in the As ion-implanted Si1-xGex epilayers. The results show that the strain relaxation mechanism of the non-implanted Si1-xGex epilayers is different from that of the As ion-implanted Si1-xGex epilayers.