InGaP Alloy Research Articles

Determination of structural parameters in heterojunction bipolar transistors by x-ray diffraction with (002) reflection

Both GaAs and InP heterojunction bipolar transistors (HBT’s) were analyzed by x-ray diffraction measurements with (002) reflection. For GaAs HBT’s, the InGaP emitter thickness and alloy composition were accurately determined. For InP HBT’s, both the base and emitter layer thicknesses could be extracted. Thickness determined from x-ray diffraction measurements agreed well with that measured by transmission electron microscopy.

Optical and structural characterization of LP MOVPE grown lattice matched InGaP/GaAs heterostructures

Lattice matched InGaP alloys grown by Low Pressure Metal Organic Vapor Phase Epitaxy were studied by Atomic Force Microscopy, X-ray diffraction, microRaman spectroscopy and Photoluminescence mapping. The study is devoted to the analysis of both the composition fluctuations and spontaneous CuPt-type order. N-type (Si-doped) and semi-insulating substrates were used. Order seems to occur in a higher amount in layers grown on Si-doped substrates; the morphology and the properties of the layers are shown to depend on the type of substrate. The Raman study of the layers allows to establish the influence of CuPt-type order on the Raman spectrum of lattice matched InGaP. The relation between the Raman parameters and the spontaneous CuPt-type order is discussed.

Photoluminescence investigation of superlattice ordering in organometallic vapour phase epitaxy grown InGaP layers

InGaP alloys, lattice matched to GaAs (100), were grown in different organometallic vapour phase epitaxy reactors operating at low pressure. cw-photoluminescence spectroscopy was used to investigate the role of growth temperature, substrate misorientation and doping on the ordering effect. The bleaching of the exciton peak and a strong thermal quenching of the PL efficiency was observed in different samples. The line-shape analysis of PL spectra obtained at different temperatures and excitation intensities confirmed the band gap dependence on the ordering effect; a maximum band gap reduction (BGR) of ∼109 meV was observed, corresponding to an order parameter η=0.47, obtained for nominally undoped layers grown at 640 °C on GaAs (100) substrates, 2° misoriented toward the (110) direction. A weak dependence of such maximum on degree and direction of the substrate misorientation seems to be possible; the temperature dependence of the PL peaks resulted the weaker the higher the ordering presence. In the case of both n- and p-type doped InGaP layers, the effect of doping in reducing both the ordering formation and the average size of ordered domains was confirmed.

Exciton Diamagnetic Shifts and Magnetic Field Dependent Linewidths in Ordered and Disordered InGaP Alloys

AbstractWe have measured the diamagnetic shifts and photoluminescence linewidths of excitonic transitions in ordered and disordered In0.48 Ga0.52 P alloys, lattice matched to GaAs, in pulsed magnetic fields at 4 and 76K. The pulsed magnetic field ranged between 0 and 50T. The variations diamagnetic shifts with magnetic field in disordered and weakly ordered samples are considerably smaller than those calculated using a free exciton model. For a given magnetic field, the value of the diamagnetic shifts are found to increase with increasing order parameter. Furthermore, for all samples, the diamagnetic shifts at 76K are larger than at 4K suggesting that the excitons are strongly localized.

InGaP/GaAs based heterojunction bipolar transistor characterisation using non-contact optical spectroscopy

In this work we have characterised InGaP/GaAs based heterojunction bipolar transistor (HBT) structures, fabricated by metalorganic chemical vapour phase epitaxy (MOVPE), using non-contact electro-optic spectroscopic techniques, photoreflectance (PR), photoluminescence (PL) and ellipsometry. PR analysis details both band structure and interfacial electric field data for both the GaAs collector and InGaP emitter regions. Including sub-lattice ordering for the InGaP alloy, the PR analysis also indicates the presence of an interfacial or intermixing layer between the emitter and GaAs base as a result of non-optimal MOVPE growth. The results are compared with room temperature PL spectra, demonstrating in particular the modification to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental data are also supported with finite-element device simulation, showing the effect of mixing layers on the interfacial band potentials. To interpret the experimental HBT ellipsometric response it was found necessary to include InGaP/GaAs layer intermixing within the optical model, consistent with the previous data. The implications of these results for HBT device performance are also discussed.

Self-Organized Dot/Columnar Structures and Quasi-Perfect CuPt-Type Ordering in (GaP)n(InP)n Superlattices Grown on GaAs (N11) Substrates by Gas Source Molecular Beam Epitaxy

(GaP)n (InP)n short-period superlattices (SLs) are grown on GaAs (N11) and (100) substrates by gas source molecular beam epitaxy. Transmission electron microscopy observations show that the SLs grown on GaAs (311)A and (411)A have lateral-composition-modulated dot/columnar structures with a lateral period of about 10–20 nm, while on GaAs (100), wire structures are formed. Photoluminescence (PL) peak energies are greatly dependent on substrate orientation and monolayer number n corresponding to the lateral composition modulation. On the other hand, the (GaP)n (InP)n SLs grown on GaAs (111) have no lateral composition modulation for n≤4 and have quasi-perfect CuPt-type ordering along the <111> growth direction for n=1, where the PL peak energy is 321 meV lower than that of disordered InGaP alloy. Quantum dots formed in (GaP)2(InP)2.5 SL/ In0.49Ga0.51P multilayers by self-organization exhibit strong 77 K PL with a full width at half-maximum of about 70 meV. Anomalous temperature variation of PL peak energy is observed in these self-organized structures.

Ordering and Phase Separation in Movpe Ingap Alloys and Unicompositional Quantum Wells

The microstructures of In{sub 0.5}Ga{sub 0.5}P alloys grown on (100) GaAs by MOVPE have been characterized with cross-section TEM and their optical emission examined with photoluminescence at low temperatures. All the alloys exhibit spinodal-like decomposition with compositional modulations along directions in the growth plane. Alloys grown at 775C have the highest emission energy, 2.0 eV, while those at 675C have the lowest, 1.89 eV, due to strong CuPt-type ordering of In and Ga. The ordered domains are platelets 20 to 200 nm wide and 10--20 nm thick with antiphase boundaries 1--2 nm apart. We have also formed ``unicompositional`` quantum wells of thin (1.3--20 nm) ordered layers grown at 675C between disordered barriers grown at 775C. Ordering is found only in the active layer, with domains similar to those of thick layers. The emission energy increases by 90 meV as the well thickness is decreased from 10 to 1.3 nm, thus demonstrating quantum size effects solely through disorder-order phenomena.

Thermal quenching of Er3+-related luminescence in In1−xGaxP

Thermal quenching of the characteristic intracenter luminescence from trivalent Er ions in In1−xGaxP layers was investigated. The Er-doped InGaP alloys were prepared by metalorganic vapor phase epitaxy with compositions ranging from x=0 to 0.31. A thermally activated luminescence quenching was observed with an activation energy that depended on the alloy composition. From measurements of the thermal quenching of the photoluminescence, the energy level of an erbium-related trapping center in the alloys was determined. The variation of the position of the Er-related energy level as a function of alloy composition is explained in terms of a vacuum-referred binding energy model.

Graded InGaP Schottky diodes on Si-doped InP

A compositionally graded InGaP alloy layer grown on a Si-doped InP layer was used to enhance the Schottky barrier height of InP. The fabricated diodes were characterized by Auger depth profiling, variable temperature I-V, capacitance-voltage (C-V), and internal photoemission. Rectification behavior with a low leakage current was achieved (J=8.3×10−7 A/cm2 at −1V). An enhanced Schottky barrier height of 1.18 eV was measured. The large barrier height permitted a reliable C-V profile of a moderately doped InP layer (7×1017 cm−3).

Comparative study of atomic ordering and alloy clustering in InGaP crystals grown by metalorganic vapor phase epitaxy, chloride-vapor phase epitaxy, and liquid phase epitaxy

We describe the results of the transmission electron microscope study of ordered and modulated structures in InGaP alloy semiconductors grown on (001) GaAs substrates by metalorganic vapor phase epitaxy, chloride-vapor phase epitaxy, and liquid phase epitaxy. Strong ordering of CuPt-type has been observed in InGaP grown by metalorganic vapor phase epitaxy at 630 °C, which is associated with an abnormality in the photoluminescence peak energy. CuPt-type ordered structures have also been observed in crystals grown by chloride-vapor phase epitaxy, but the degree of ordering is weaker and crystals grown at 576–740 °C exhibit normal photoluminescence peak energies. On the other hand, in crystals grown by liquid phase epitaxy, no ordered structure is found and the crystals exhibit normal photoluminescence peak energies. There is no dependence of modulated structures on the growth method since they are observed in all crystals. These results also lead us the previous conclusion by Kondow and co-workers that the ordered structures are not generated under thermal equilibrium conditions but rather by the diffusion and reconstruction of deposited atoms on the growth surface.

Comparison of Ordered and Modulated Structures in InGaP Alloy Semiconductors grown by MOCVD, Chloride-Vpe and LPE Methods

AbstractOrdered and modulated structures in InGaP alloy semiconductors grown on (001) GaAs substrates by metalorganic chemical vapor deposition, chloride-vapor phase epitaxy, and liquid phase epitaxy have been systematically studied by transmission electron microscopy. In InGaP grown by metalorganic chemical vapor deposition at 630°C, strong ordering of CuPt-type has been observed, which is associated with an abnormality in the photoluminescence peak energy. For crystals grown by chloride-vapor phase epitaxy, CuPt-type ordered structures have also been observed. However, the degree of ordering is weaker in the latter case and crystals grown at 576-740°C exhibit normal photoluminescence peak energies. On the other hand, in crystals grown by liquid phase epitaxy, no superstructure spots are found in the electron diffraction patterns and the crystals exhibit normal photoluminescence peak energies. Modulated structures do not depend on the growth method since they are observed in all crystals. From these results, it has been concluded that the ordered structures are not generated under thermal equilibrium conditions but rather by the diffusion and reconstruction of deposited atoms on the growth surface.

Photoluminescence study on local atomic arrangements in InGaP and GaAsP alloys using Co deep impurity

Low-temperature photoluminescence (PL) related to Co deep impurities in In1−x GaxP (0.74≤x≤1) and GaAs1−x Px (0.65≤x≤1) alloys has been studied. Broad PL bands with some structures have been observed in the 2.3-μm region for both the alloys. The results of time-resolved PL measurements have shown that the PL bands are due to the intracenter transitions 4T2(4F)→4A2(4F) in a substitutional Co2+ ion in the zinc-blende lattices. These Co-related PL spectra have been analyzed in terms of the local atomic arrangements around the Co luminescent center. As a result, it has been found that these Co-related PL spectra in InGaP and GaAsP alloys are composed of several bands closely related to the local arrangement of atoms around the Co center.