Optical gain of 1.3 /spl mu/m GaAsSbN/GaAs quantum well lasers

Optical gain of 1.3 mum GaAsSbN/GaAs quantum well (QW) structure is investigated using the multiband effective mass theory. The results are compared with those of 1.3 mum InGaNAs/GaAs and GaAsSb/GaAs QW structures. The optical gain of the GaAsSbN/GaAs QW structure is found to be similar to that of the InGaAsN/GaAs QW structure. In contrast, GaAsSbN/GaAs and InGaNAs/GaAs QW structures show significantly larger optical gain than the GaAsSb/GaAs QW structure. This is mainly attributed to the fact that the former has a larger optical matrix element than the latter. In addition, GaAsSbN/GaAs and InGaNAs/GaAs QW structures have much smaller threshold current density than the GaAsSb/GaAs QW structure. This is because the Auger recombination current density gives dominant contribution to the threshold current density and the former has smaller threshold carrier density than the latter. On the contrary, the threshold current density of the GaAsSbN/GaAs QW structure is shown to be similar to that of the InGaAsN/GaAs QW structure     

Zinc blende GaAsSb nanowires grown by molecular beam epitaxy

We report the growth of GaAsSb nanowires (NWs) on GaAs(111)B substrates by Au-assisted molecular beam epitaxy. The structural characteristics of the GaAsSb NWs have been investigated in detail. Their Sb mole fraction was found to be about?25%. Their crystal structure was found to be pure zinc blende (ZB), in contrast to the wurtzite structure observed in GaAs NWs grown under similar conditions. The ZB GaAsSb NWs exhibit rotational twins around their [111]B growth axis, with twin-free segments as long as 500?nm. The total volumes of GaAsSb segments with twinned and un-twinned orientations, respectively, were found to be equal by x-ray diffraction analysis of NW ensembles.     

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T _C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T _C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.     

Temperature stability of photoluminescence in heterostructures with InGaAs/GaAs quantum well and Mn-delta-doped acceptor layer in GaAs barrier

The temperature dependence of the electro- and photoluminescence of heterostructures with InGaAs/GaAs quantum well and a closely spaced manganese delta (δ)-doped layer in the GaAs barrier was investigated. It is found that the proposed heterostructures exhibit increased temperature stability and decreased temperature quenching as compared to the control structures containing no δ-doped layers. An increase in the operating temperature is explained by the appearance of an additional potential barrier for electrons due to the δ-doped acceptor layer formation in the near-surface barrier.     

Influence of Sb/As soak times on the structural and optical properties of GaAsSb/GaAs interfaces

The effects of Sb/As soak times, prior to growth of GaAsSb on GaAs were investigated by High Resolution X-Ray Diffraction (HRXRD) and photoluminescence (PL). Multiple quantum well samples with soak times of 0 s, 30 s and 60 s were grown at 500 °C with nominally identical Sb and As fluxes. HRXRD results show that a 30 s soak minimizes diffuse scattering seen around superlattice peaks in the reciprocal space maps, an effect attributed to corrugations in the GaAs-GaAsSb interface. An inferred band diagram calculated using a four band k.p model and modified taking into account the HRXRD results was used to explain PL spectra taken for each sample at 80 K. It is concluded that an optimum soak time exists for GaASb growth on GaAs, determined by the growth conditions.     

Modeling of In segregation, stress and strain in InGaAs/GaAs(100) quantum well heterostructures

An advanced model for simulation of In segregation phenomena, stress and strain distribution during metal-organic chemical vapor deposition of InGaAs/GaAs(100) quantum well (QW) heterostructures based on representation of boundary gas layer as “quasi-liquid” has been suggested. Elastic energy was taken into account by considering epitaxy as a sequence of growth acts each resulted in the formation of ultrathin imaginary layers. The assumption that elastic influence is not distributed throughout the whole thickness of the substrate but affects only its near-surface layer has been postulated. Results of calculations of In profiles and stress distribution for heterostructures with single and multiple QWs for varied epitaxy conditions are provided. Various options of exploring the developed model for other materials and the limitations of applicability are discussed.     

Room-temperature photoconductivity in the 1–2.6 µm range in InAs/GaAs heterostructures with quantum dots

We have studied the room-temperature photoconductivity in the wavelength range 1–2.6 μm in InAs/GaAs heterostructures with quantum dots (QDs). Specific features of these heterostructures grown using the metalorganic vapor phase epitaxy (MOVPE) were an increase in the amount of InAs during the formation of a sheet of QDs and the use of alternating low-and-high-temperature regimes during their overgrowth with a GaAs barrier layer. For the first time, the MOVPE-grown multilayer InAs/GaAs heterostructures with quantum dots exhibited photoluminescence in a wavelength range of up to 1.6 μm and the photoconductivity up to 2.6 μm at room temperature. The heterostructures exhibited a room-temperature voltage sensitivity of 3 × 10³ V/W (within a Si-plate filter bandwidth) and a specific detectivity of 9 × 10⁸ cm Hz^1/2 W^?1.     

Long-wavelength emission in InGaAsN/GaAs heterostructures with quantum wells

The properties of InGaAsN/GaAs heterostructures with quantum wells on GaAs substrates were studied. The GaAsN layers containing InGaAsN quantum wells with a high (exceeding 1%) nitrogen concentration were obtained. The long-wavelength emission in the InGaAsN quantum wells is obtained in the wavelength range up to 1.32 μm at room temperature. The effect of the InGaAsN quantum parameters on the optical properties of heterostructures is studied.     

The current–voltage characteristics of heterostructures formed by MEH-PPV spin-coated on n-type GaAs and n-type porous GaAs

P–N heterostructures are formed by depositing the poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) MEH-PPV on n-type GaAs(100) substrate and on n-type porous GaAs. The elaborated heterostructures are studied by current–voltage measurements. Thermionic emission is used to model the heterostructures behaviors and to extract parameters as ideality factor and zero bias barrier high. Such model also appears to be useful as a new approach for calculating hole concentration in MEH-PPV deposited on n-type GaAs (N_a = 2.2 × 10¹⁷ cm^− 3). The zero bias barrier height in both heterostructures were found to be close to the ionization energy difference of isolated MEH-PPV and n-type GaAs and the ideality factor values are found to be high. Such high values are suggested to be due to the existence of high density of trap. This is preliminary evidenced by calculating the trap density using space charge limited conductivity (SCLC) characterized by an exponential distribution of trapping levels in both heterostructures.     

Reliability and degradation of 980 NM InGaAs/GaAs strained quantum well lasers

Degradation behaviours of 980 nm InGaAs/GaAs strained quantum well (QW) lasers are clarified and compared with normal AlGaAdGaAs, InGaAsP/InP and GaAs/GaAs QW lasers. Through various ageing tests, it is confirmed that 980 nm InGaAs/GaAs strained QW lasers are applicable to optical fibre transmission systems where the components are required to be highly reliable.     

MOCVD 生长及 TEM 表征 GaAs/Al_xGa_(1-x)As 量子异质结构材料

本文报道 MOCVD 生长 GaAs/Al_xGa_(1-x)As 量子异质结构材料(超晶格、量子阱及量子共振隧穿二极管),采用横断面透射显微术表征了样品的界面结构。实验表明:多量子阱与超晶格的周期性良好,层与层之间界面清晰,采用[100]带轴入射,观察到超晶格的 TEM 卫星衍射斑,测量到量子阱中电子的子能级跃迁吸收。研究了生长工艺和材料结构的关系,分析了影响 RT 器件的因素。     

Temperature dependence of optical transitions in AlxGa1–xAs/GaAs quantum well structures grown by molecular beam epitaxy

Quantum well (QW) structures of Al_xGa_1–xAs/GaAs were characterized by photoluminescence technique as a function of the temperature between 10 and 300 K. The structures were grown on a 500 nm thick GaAs buffer layer with Molecular Beam Epitaxy technique. We have studied the properties of in-situ Cl₂-etched GaAs surfaces and overgrown QW structures as a function of the etching temperature (70 and 200 °C). Several models were used to fit the experimental points. Best fit to experimental points was obtained with the Pässler model.     

Structural characterization of GaSb-capped InAs/GaAs quantum dots with a GaAs intermediate layer

GaSb incorporation to InAs/GaAs quantum dots is considered for improving the opto-electronic properties of the systems. In order to optimize these properties, the introduction of an intermediate GaAs layer is considered a good approach. In this work, we study the effect of the introduction of a GaAs intermediate layer between InAs quantum dots and a GaSb capping layer on structural and crystalline quality of these heterostructures. As the thickness of the GaAs intermediate layer increases, a reduction of defect density has been observed as well as changes of quantum dots sizes. This approach suggests a promising method to improve the incorporation of Sb to InAs heterostructures.     

Photoreflectance study of strained GaAsN/GaAs T-junction quantum wires grown by metal-organic vapor phase epitaxy

Strained GaAsN T-junction quantum wires (T-QWRs) with different N contents grown on GaAs by two steps metal-organic vapor phase epitaxy in [001] and [110] directions, namely QW1 and QW2 respectively, have been investigated by photoreflectance (PR) spectroscopy. Two GaAsN T-QWRs with different N contents were formed by T-intersection of (i) a 6.4-nm-thick GaAs0.89N0.011 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2 and (ii) a 5.0-nm-thick GaAs0.985N0.015 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2. An evidence of a one-dimensional structure at T-intersection of the two QWs on the (001) and (110) surfaces was established by PR resonances associated with extended states in all the QW and T-QWR samples. It is found that larger lateral confinement energy than 100 meV in both of [001] and [110] directions were achieved for GaAsN T-QWRs. With increasing temperature, the transition energy of GaAsN T-QWRs decreases with a faster shrinking rate compared to that of bulk GaAs. Optical quality of GaAsN T-QWRs is found to be affected by the N-induced band edge fluctuation, which is the unique characteristic of dilute III-V-nitrides.     

Fermi-edge singularity in photoluminescence spectra of modulation-doped AlGaAs/InGaAs/GaAs quantum wells

The photoluminescence study of Fermi-edge singularity (FES) in modulation-doped pseudomorphic Al _x Ga_1?x As/In _y Ga_1?y As/GaAs quantum well (QW) heterostructures is presented. In the above QW structures the optical transitions between n = 1 and n = 2 electronic subband to the n = 1 heavy hole subband (E ₁₁ and E ₂₁ transitions, respectively) are observed with FES appearing as a lower energy shoulder to the E ₂₁ transition. The observed FES is attributed to the Fermi wave vector in the first electronic subband under the conditions of population of the second electronic subband. The FES appears at about 10 meV below E ₂₁ transition around 4·2 K. Initially it gets stronger with increasing temperature and becomes a distinct peak at about 20 K. Further increase in temperature quenches FES and reaches the base line at around 40 K.     

Circularly polarized electroluminescence of quantum-size InGaAs/GaAs heterostructures with ferromagnetic metal-GaAs Schottky contacts

Electroluminescence (EL) of InGaAs/GaAs heterostructures with quantum wells and ferromagnetic metal (Co, Ni)/GaAs Schottky contacts has been studied in magnetic fields up to 10 T at a temperature of 1.5 K. The EL line corresponding to the recombination of electrons with injected holes exhibits splitting into components corresponding to the Landau levels in the applied magnetic field and shows circular polarization that significantly exceeds the level typical of such structures with nonmagnetic (Au/GaAs) contacts. The degree of circular polarization (P _EL) exhibits a nonmonotonic dependence on the applied magnetic field and is correlated with the filling of Landau levels. The maximum degree of circular polarization reached in the heterostructures studied is P _EL = 40%.     

Forming interface in Pd/Fe/GaAs/InGaAs structure for optical detector of free-electron spin

Conditions necessary for the formation of a Fe/GaAs interface have been established and the electrical, magnetic, and optical properties of Pd/Fe/GaAs heterostructures with InGaAs quantum wells have been studied. The possibility of obtaining an epitaxial layer of Fe on GaAs(001) surface at room temperature is demonstrated. The magnetization curve of Fe layer exhibits hysteresis with an easy axis in plane of the sample. Iron exhibits surface segregation by diffusion through a 4-nm-thick Pd layer. The properties of obtained Pd/Fe/GaAs/InGaAs structures show evidence for their possible use in optical detectors of free-electron spin.     

Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well

Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4?K) time-resolved PL measurements show a decay time of [Formula: see text]?ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text]?ns).     

GaAsN/GaAs and InGaAsN/GaAs heterostructures grown by molecular beam epitaxy

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 μm radiation at room temperature was demonstrated using In_0.28Ga_0.72As_0.97N_0.03/GaAs quantum wells. Pis’ma Zh. Tekh. Fiz. 24, 81–87 (December 12, 1998)     

Orientation-dependent phase separation of GaAsSb epilayers grown by gas-source molecular-beam epitaxy

This work describes a regular solution model that considers the free energy of the surface monolayer to explain the orientation-dependent phase separation in GaAsSb. In the proposed model, only the interaction between the second nearest-neighboring atoms sitting on the same monolayer contributes to the interaction parameter. Consequently, the parameter reduces to Ω/2 and Ω/3 for (111)B GaAsSb and (100) GaAsSb, where Ω denotes the parameter of bulk GaAsSb. By including the strain effect, the proposed model thoroughly elucidates the immiscibility behavior of (111)B GaAsSb and (100) GaAsSb.