InGaAsP Alloys Research Articles

Novel Fabrication of C-Doped Base InGaAs/InP DHBT Structures For High Speed Circuit Applications

AbstractWe have fabricated InGaAs/InP based DHBTs for high speed circuit applications. A process involving both wet chemical and ECR plasma etching was developed. Carbon was employed as the p-type dopant of the base layer for excellent device stability. Both the emitter-base and base-collector regions were graded using quaternary InGaAsP alloys. The extrinsic emitter-base junction is buried for junction passivation to improve device reliability. The use of an InP collector structure with the graded region results in high breakdown voltages of 8V to IOV, with no current blocking. The entire structure is encapsulated with spin-on-glass. These devices show no degradation in DC characteristics after operation at an emitter current density of 90kA/cm2 and a collector bias, VCE, of 2V at room temperature for over 500 hours. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2 × 4 μm2 emitter size devices.

Enhancement of conduction-band effective mass in III–V semiconductor alloys induced by chemical disorder

The conduction-band effective masses in InxGa1−xAs with a complete range of composition, and InAlGaAs and InGaAsP alloys covering the complete range of lattice matched to InP have been determined by far-infrared optically detected cyclotron resonance and magnetophotoconductivity measurements. It is found that the measured effective masses as a function of alloy composition are heavier than the values predicted from the five-band k⋅p theory. We show that this discrepancy can be resolved by including the effect of disorder-induced potential fluctuations that causes the wave function mixing between conduction and valence bands. We find that the strength of the potential fluctuations can be well described in terms of the Phillips electronegativity difference related to chemical disorder.

Inhibition of thickness variations during growth of InAsP/InGaP and InAsP/InGaAsP multiquantum wells with high compensated strains

We demonstrate by using transmission electron microscopy that the insertion of small amounts of a well-chosen material lattice matched to the substrate at the interfaces between the highly strained layers of a strain-compensated multiquantum well (MQW) may prevent the catastrophic morphological degradation of the epitaxial structure as growth proceeds. For InAsP/InGaP and InAsP/InGaAsP MQWs grown on an InP substrate, we find that InP itself is an efficient interfacial material, whereas for the same InAsP/InGaAsP MQWs, an InGaAsP alloy is less effective. We show that the interfacial InP restores the planarity of the growth surface by filling the depressions of the underlying undulating strained layer.

Deposition of InGaAsP alloys on GaAs by low pressure metalorganic vapor phase epitaxy: Theory and experiments

A combined thermodynamic-kinetic approach to the epitaxial deposition of InGaAsP alloys on GaAs substrates is presented. Good agreement with experimental group V solid phase incorporation has been found when neglecting the 2V2 = V4 (V = As,P) vapor phase reactions, while the group III solid phase composition is well described by simple mass-transport limited processes. InGaAsP materials, lattice matched to GaAs, have been grown in a wide composition range toward the ternary limit [In(0.49)Ga(0.51)P]. Furthermore, high quality InGaAsP/GaAs strained quantum wells with a bandgap below that of GaAs are realized for the first time.

Effect of temperature on InGaAsP alloy composition

The influence of growth temperature on the composition of InGaAsP films grown by low pressure metalorganic vapor phase epitaxy (MOVPE) is reported for quaternary (Q) alloys having bandgap wavelengths of λg = 1.1, 1.3, and 1.5 μn. Films with these different Q-compositions were deposited lattice matched to InP at a growth temperature of 675°C. Subsequent growth experiments were then performed for each Q-composition in which the input gas flow rates were kept the same and only the temperature changed in 25°C decrements down to 600°C. Photoluminescence (PL) and lattice mismatch (LMM) measurements of the resulting films were used to determine the effect of growth temperature on film composition. The PL data indicate a temperature shift in the PL wavelength of −1.8 nm/ °C for the 1.5Q composition, −2.9 nm/°C for 1.3Q, and −4.3 nm/°C for 1.1Q. Negative shifts were also observed in LMM of −80 ppm/°C for 1.5Q, −150 ppm/°C for 1.3Q, and −250 ppm/°C for 1.1Q. The Ga/In and P/As ratios of the Q-filmswere measured by secondary ion mass spectroscopy and correlated with full-wafer maps of the PL wavelength and lattice mismatch to gain insight into the processes responsible for wafer nonuniformity in MOVPE.

Refractive index and loss changes produced by current injection in InGaAs(P)-InGaAsP multiple quantum-well (MQW) waveguides

We have theoretically estimated the carrier-induced changes in the refractive index /spl delta/n and the optical loss /spl delta//spl alpha/ produced by the injection of free carriers in InGaAs(P)-InP multiple quantum-well (MQW) optical waveguides. MQW structures are specially designed for the tuning layer in carrier injection type tunable laser diodes, such as tunable twin-guide laser diode (TTG-LD), at the lasing wavelength /spl lambda/ of 1.55 /spl mu/m. Anomalous dispersion and plasma effect for /spl delta/n and IVBA (intervalance band absorption) for /spl delta//spl alpha/ were included. A valance-band mixing, an overlap integral of electron-hole, and confinement factors of carriers in the well were considered to include quantum-size effect of carriers in /spl delta/n and /spl delta//spl alpha/. Predictions of /spl delta/n are in reasonably good agreement with the experimental results. Systematic analysis shows that the following InGaAs(P)(well)-InGaAsP (barrier) MQW structures ace promising in order to obtain a large /spl delta/nat a given injection current density J: 1) well materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.55 /spl mu/m, 2) barrier materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.4 /spl mu/m, 3) as many as possible number of wells, typically about 15./spl delta//spl alpha/ is also estimated by calculating the carrier distributions in MQW structures and by fitting experimental data of bulk and MQW waveguides. The maximum well number is limited by the increase of optical loss. According to these results, we have found that 1.55-/spl mu/m InGaAsP (well 1.8-nm thick)/1.40 /spl mu/m InGaAsP (barrier 14-nm thick) MQW, with the well number of around 15, will be the optimum tuning layer structure for 1.55-/spl mu/m band tunable LD's. Over 10 nm continuous tuning range, with moderate output power, is expected for TTG-LD's. >

0.98-μm InGaAs-InGaP strained quantum-well lasers with GaAs-InGaP superlattice optical confinement layer

We have proposed a GaAs-InGaP superlattice optical confinement layer (SL-OCL), which replaces graded InGaAsP alloy layers in 0.98-/spl mu/m InGaAs-InGaP graded-index separate-confinement-heterostructure (GRINSCH) strained quantum-well (QW) lasers. Theoretical study of the multiquantum barrier (MQB) effect of the GaAs-InGaP SL indicates that electrons in the GaAs OCL feel more than two times higher barrier height than the classical bulk barrier height. Actually, the increase of internal quantum efficiency and the decrease of threshold current density were confirmed. Furthermore, the extremely high characteristic temperature T/sub 0/ of 300 K around RT was obtained. These improvements of laser characteristics, especially high T/sub 0/, is mainly owing to the enhancement of the carrier confinement due to the MQB effect of the SL-OCL. >

Characterization of high quality InGaP/GaAs and InGaAsP/GaAs heterostructures grown by low pressure metal-organic chemical vapour deposition

A thermodynamic approach to the epitaxial deposition of InGaAsP alloys onto GaAs substrates was reviewed, and good agreement was found with experiments when neglecting the 2 V 2 = V 4 ( V = As, P) vapour phase reaction. InGaAsP and its ternary limit InGaP were grown at different temperatures, substrate misorientation and V-III ratios. X-ray diffraction techniques and photoluminescence were employed to assess the quality of the materials grown.

High-power laser diodes based on InGaAsP alloys

HIGH-POWER, high-coherence solid-state lasers, based on dielectric materials such as ruby or Nd:YAG (yttrium aluminium garnet), have many civilian and military applications. The active media in these lasers are insulating, and must therefore be excited (or ‘pumped’) by optical, rather than electrical, means. Conventional gas-discharge lamps can be used as the pumping source, but semiconductor diode lasers are more efficient, as their wavelength can be tailored to match the absorption properties of the lasing material. Semiconducting AlGaAs alloys are widely used for this purpose1, 2, but oxidation of the aluminium and the spreading of defects during device operation limit the lifetime of the diodes3, and hence the reliability of the system as a whole. Aluminium-free InGaAsP compounds, on the other hand, do not have these lifetime-limiting properties4–8. We report here the fabrication of high-power lasers based on InGaAsP (lattice-matched to GaAs substrates), which operate over the same wavelength range as conventional AlGaAs laser diodes and show significantly improved reliability. The other optical and electrical properties of these diodes are either comparable or superior to those of the AlGaAs system.

980-nm aluminum-free InGaAs/InGaAsP/InGaP GRIN-SCH SL-QW lasers

The design of 980-nm InGaAs/InGaAsP/InGaP GRIN-SCH lasers with aluminium-free GaAs-based materials is discussed. The first approach was successful MOCVD growth of InGaAsP alloy lattice matched to GaAs. It was found that an immiscible region existed, as determined by photoluminescence measurements. The main approach was to introduce the graded bandgap structure consisting of InGaAsP layers lattice matched to GaAs into GaAs/InGaP interfaces. The graded structure suppresses the heterojunction spikes, especially of the valence band at these interfaces. As a result, series resistance of GRIN-SCH lasers with the graded bandgap structure was reduced compared with simple SCH lasers with abrupt bandgap interfaces due to improved hole injection. Furthermore, the optimum graded structures for optical confinement region were investigated to improve the carrier injection efficiency, especially electron injection efficiency into a single quantum well active layer. Also, this graded bandgap structure formed the graded refractive index profile in an active region, which is the so-called GRIN-SCH waveguide. The GRIN-SCH profile could be controlled to narrow the transverse beam divergence for high coupling efficiency into a single-mode fiber and to reduce the optical power density at facets for high reliability. Finally the results of a life-test of GRIN-SCH lasers was shown, and the lifetime of GRIN-SCH lasers with immiscible InGaAsP layers was discussed. >

Electron microscopy and mass-spectrometry study of In0.72Ga0.28As0.62P0.38 lasers grown by liquid phase epitaxy

Broad area as well as buried heterostructure lasers based on In0.72Ga0.28As0.62P0.38/InP and emitting at 1.3 μm are grown by liquid phase epitaxy and are studied in detail by means of transmission electron microscopy, X-ray diffraction, secondary ion mass-spectrometry, and electroluminescence. The InGaAsP epilayer is found to be well lattice-matched and of good structural quality. A tentative explanation is presented for the spinodal decomposition observed in the InGaAsP alloy. We also report on the high performance characteristics of the infrared lasers.

Electron microscopy and mass-spectrometry study of InGaAsP/InP heterostructures (pin diodes) grown by liquid phase epitaxy

Large area InGaAsP/InP double heterostructures for λ = 1.3 and 1.55 μm applications grown by liquid phase epitaxy are studied in detail by means of transmission electron microscopy, high resolution electron microscopy, X-ray diffraction, secondary ion mass-spectrometry, and photoluminescence. The InGaAsP epilayers are found to be well lattice matched and of excellent structural quality. A qualitative explanation is provided for the spinodal decomposition observed in the InGaAsP alloy for λ = 1.3 μm. The high performance characteristics of the infrared photodiodes based on this double heterostructure are reported as well.

Growth of semi-insulating InGaAsP alloys using low-pressure MOCVD

Semi-insulating Fe-doped InGaAsP alloys of λ = 1.0, 1.15, 1.35 and 1.55 μm wavelength compositions lattice matched to InP have been grown and characterized for the first time. The resistivity is maximum for λ = 1.0 μm InGaAsP at a value of 1×10 8 ω cm, and decreases exponentially with the arsenic mole fraction for the longer wavelength alloys. The solubility of Fe in the InGaAsP is fixed at the InP solubility value of 5×10 16 cm −3 at 630°C until phosphorus is eliminated from the alloy lattice. Diffusion of Fe in InGaAsP is noted, where the diffusion tendency increases with the arsenic mole fraction. Limiting the total Fe concentration to the solubility limit of Fe in InGaAsP greatly reduces diffusion of Fe.

Vapor phase epitaxy of InGaAsP by the chloride single flat temperature zone method

The VPE growth of InGaAsP alloy using the chloride single flat temperature-zone (SFT) method is described. The basic data, such as growth kinetics, optical and electrical properties, of InGaAsP layers grown by the chloride SFT method are shown. It is seen that the chloride SFT method provides good crystalline InGaAsP layer reproducibly. The same slow kinetic process as in other III-V compounds and alloys limits the rate of the InGaAsP growth. Moreover, InGaAsP/InP heterostructure is prepared, and a photoluminescence peak width as narrow as 13.5 meV at 4.2 K is obtained, from 100 Åsingle quantum well.

Defect Generation and Suppression During the Impurity Induced Layer Disordering of Quantum Sized GaAs/GalnP Layers

Impurity induced layer disordering (JILD) has been demonstrated as an extremely powerful technique for the fabrication of optoelectronic devices within the AlGaAs alloy system. The success of this technique in this material system is due in large part to the similarity of the lattice parameters between the two binary constituents in this system, AlAs and GaAs. There are many alloy systems in which it would be highly desirable to exploit the fabrication technique of JILD, but within which the binary alloy constituents are not so well matched in lattice parameter. Perhaps the most extensively explored of such systems are the AlGaInP alloy system lattice matched to a GaAs substrate and the InGaAsP alloy system lattice matched to an InP substrate.

Thermal degradation of InP in open tube processing: deep-level photoluminescence

Thermal processing of InP at temperatures above 500 °C is indispensable in the growth and device fabrication of InGaAsP alloy semiconductors for optoelectronic and microwave applications. Incongruous loss of P at these temperatures creates native defects and their complexes. The presence of such defects modifies the electrical and optical properties of the material resulting in poor device performance. In addition, native defects play a significant role in dopant diffusion which is a topic of current interest. We have measured deep-level photoluminescence (PL) on undoped InP after heat treatments at 500 and 550 °C in an open-tube processing system in different protective environments of powder InP, and Sn-InP melt together with an InP cover. In this paper we shall present the PL results which have bearing on the question of defects. We find that (1) the Sn-InP melt provides better protection in preserving the overall luminescence in InP; (2) the deep-level PL related to defects has at least two components in the virgin samples, viz., MnIn, and band C, which is a native defect complex related to VP; (3) a new defect appears in samples heated in a P-deficient environment; and (4) the enhancement in the deep-level luminescence intensity after heat treatment can be attributed to the excess defect concentrations existing under nonequilibrium conditions of an open-tube processing environment.

Photothermal deflection spectroscopy of heat-treated GaAs, InP, and InGaAsP alloys

Photothermal deflection spectroscopy is used to study the effect of heat treatment in bulk GaAs, InP, and epitaxial InGaAsP grown on InP. We show that increased sub-band-gap absorption is related to damage near the surface. We also show that from a measurement of the phase we can differentiate between purely surface and near-surface damage.

Effective mass of holes in quaternary InGaAsP alloys lattice-matched to InP

Abstract Rapid growth of optical communications technology over the last decade is largely due to the development of InGaAsP/InP light sources and detectors whose operating wavelengths match the low-loss and low-dispersion windows of silica fibers. Proper design of such devices is, to a large extent, conditional upon the detailed knowledge of relevant material characteristics. In spite of intensive studies of InGaAsP quaternary alloy semiconductors prompted by their practical applications,1–4 there remain a number of important parameters for which only rough estimates are available. Such is the case of the heavy-hole effective mass, which is one of the least-known parameters even in the case of the binary InP.

High-temperature preservation of InP surface corrugations for distributed feedback lasers

Consistent preservation of 〈01̄1̄〉-oriented grating corrugations with 2850-Å period and 1500-Å height on (100) InP substrates has been achieved during thermal cycling at 660 °C for 60 min in a H2 ambient, using roughened GaAs cover slices. It is found that transport of Ga and As causes the formation of a graded 25-Å-thick InGaAsP alloy on the surface of the gratings, as detected by Auger and x-ray photoelectron spectroscopic analysis. This preservation technique eliminates the need for lower-temperature crystal growth of distributed feedback laser wafers by liquid-phase epitaxy (LPE). Successful growth of distributed feedback laser wafers using conventional high-temperature LPE is demonstrated.

New reactor design for growth of InP and related alloys

A new reactor has been designed for atmospheric pressure MOVPE growth of InP and InGaAsP alloys. This has a chimney geometry with a sidearm added for susceptor rotation and fully mechanized substrate loading. A high aspect ratio rectangular body permits growth on a 50 mm diameter wafer with relatively high gas velocities at modest flows. A two-step growth of InP on GaAs substrates has been used to evaluate thickness uniformity in this reactor. Two flow regimes have been identified from this study. At low flows, thermal buoyancy effects are important and the growth uniformity is improved by use of a dense carrier gas (N2H2 mixture) and cooling of the reactor wall opposite the substrate. At high flows the best thickness uniformity is obtained with a pure H2 carrier gas without the opposite wall cooling.