The origin of the long-wavelength (100–300 nm) quasi-periodic microstructure observed in transmission electron microscopy studies of spinodally decomposed In Ga1−x As y P1−y alloys has been investigated. The contrast is well explained by diffraction effects arising from lattice plane bending near the surfaces of the thinned specimens, such as would be induced by elastic relaxation of shear stresses accompanying a quasi-periodic lattice modulation. Excellent qualitative agreement between calculated and experimental contrasts lends weight to the claim that these contrasts, observed over part of the composition range of liquid phase epitaxy grown InxGa1−xAs y P1−y alloys, are associated with spinodal decomposition. The accompanying strain modulation amplitude is of the order of 10−3. It is suggested that speckle contrast on a smaller scale (5–15 nm) in this material may also be related to composition variations. More generally, the nature of near-surface elastic relaxation in compositionally modulat...

On elastic relaxation and long wavelength microstructures in spinodally decomposed InxGa1-x.AsyP1-y epitaxial layers

The elastic strain and stress fields and the elastic energy of the system composed of a crystalline epitaxial layer of finite thickness coherently grown on a bulk substrate are calculated, when the intrinsic stress‐free lattice parameter of the layer is modulated along directions parallel to the substrate surface. When the modulation has components with spatial periods of the same order as the thickness of the layer, the elastic energy is considerably reduced with respect to the same modulation occurring in a bulk sample. There exists an optimal period of elementary sinusoidal modulation, proportional to the layer thickness. Consequently, for immiscible alloys where changes of composition induce changes of intrinsic lattice parameter, the critical temperature (below which they become thermodynamically unstable with respect to composition modulations) is much higher (and the domain of instability larger) if the material is in the epitaxial layer form than in the bulk form. This extends Cahn’s theory of spinodal decomposition to epitaxial layers. It is also pointed out that if a modulation has started to occur in a growing layer, the elastic deformation induced near the free surface should have important consequences on the subsequent growth of this layer. These results are applied to III‐V semiconductors immiscible alloys, such as In x Ga1−x As y P1−y , where such composition modulations are known to exist. New values of the critical temperatures for these alloys are calculated and compared with lower former estimates. The mode of development of these modulations is discussed in light of previous experimental results and these new calculations.

Elastic state and thermodynamical properties of inhomogeneous epitaxial layers: Application to immiscible III‐V alloys

A new high-performance 1.3-μm InGaAsP semiconductor laser is described, in which effective current confinement into the active region has been realized. A p-n-p-n current blocking structure is made by liquid-phase epitaxy (LPE) on both sides of the active-stripe mesa which is defined by a pair of channels in the double-heterostructure wafer. The double-channel-planar-buried-heterostructure laser diodes (DC-PBH LD's) exhibit high-laser performances, such as a high differential quantum efficiency of 78-percent maximum, which results in high electrical to optical power conversion efficiency 43 percent, and high light output power of over 50 mW, as a result of the improvement in the current blocking structure. The threshold current temperature sensitivity is found experimentally to be reduced remarkably by increasing the doping concentration in the p-cladding layer. Characteristic temperature as high as 100 K has been obtained. CW operation is possible up to 130°C.

InGaAsP double-channel- planar-buried-heterostructure laser diode (DC-PBH LD) with effective current confinement

Wavelength shift during the period of direct modulation (dynamic wavelength shift) for injection lasers having a BH structure has been investigated both experimentally and theoretically. A GaInAsP/InP BH laser emitting a nominal wavelength of 1.61 μm was modulated by a sinusoidal current at frequencies in the range of 0.2-2 GHz. The full width of the dynamic wavelength shift was 0.35 nm at a modulation frequency of 1.8 GHz, and a modulation depth of 63 percent at a bias current 1.14 times the threshold current. It was found that the width of the dynamic wavelength shift increases with proportion to the modulation depth, and with inverse proportion to the bias current at a frequency below 1 GHZ. The differential coefficient dn/dN of refractive index n for carrier density N in the active region was measured for the purpose of the analysis. The value obtained is -1.2 \times 10^{-20} cm3. The dynamic shift of the lasing wavelength was found to be characteristic of the change of the refractive index induced by the oscillation of carrier density in the active region during intensity modulation. The theoretical shift shows maximum value at a resonance-like modulation frequency. The peak height of the resonance wavelength shift is strongly affected by carrier diffusion in the transverse direction, and has a minimum value when stripe width is nearly equal to carrier diffusion length.

Wavelength variation of 1.6 &#181;m wavelength buried heterostructure GaInAsP/InP lasers due to direct modulation

Phase diagrams of InGaAsP, InGaAs and InP lattice-matched to (100)InP

The buried-heterostructure, in which the quaternary active layer is completely surrounded by InP crystal, has been realized in 1.5 µm region by low temperature liquid phase epitaxial growth. Low threshold current of 25 mA under CW operation was achieved at 26°C. This is the lowest value so far reported on the InP/GaInAsP laser in 1.5 µm wavelength region.

InP/GaInAsP Buried Heterostructure Lasers of 1.5 µm Region

Liquid phase epitaxy (LPE) and the properties of high purity GaInAs layers on (100)InP substrates are reported. Low carrier concentration (3.8–5.4×1014 cm-3) and high electron mobility (47000–51000 cm2/V.s at 77 K) were obtained reproducibly. The influence of source Ga-In-As melt baking temperatures on the epitaxial layer purity was investigated. The results of a photoluminescence study and van der Pauw measurements show that acceptor impurities as well as donor impurities can be excluded from the source solution by a suitable heat treatment.

Effect of Baking Temperature on Purity of LPE Ga0.47In0.53As

Liquid phase epitaxial (LPE) growth of In1-xGaxAs1-yPy crystals lattice matched to InP was studied systematically with a controlled amount of supersaturation for whole range of composition at relatively low temperature (590°C) A region of extremely slow growth rate was found for the quaternary crystal with 135 µm band-gap and surfaces of quaternary layers became rough around 144 µm The growth rate of the crystals around 135 µm was found to be relatively slow even when the growth temperature is 640°C Comparison of these phenomena with those observed in AlGaAsSb system suggests the existence of immiscible region in this system below 600°C

Instability of In-Ga-As-P Liquid Solution during Low Temperature LPE of In1-xGaxAs1-yPy on InP

The 1.5 µm InGaAsP/InP lasers on p-type InP substrates have been realized by a simple fabrication process. By utilizing buried-heterostructure, a low threshold current of 40 mA under cw operation and a large operating current range, 1 A, were achieved

1.5 µm InGaAsP/InP BH Lasers on p-Type InP Substrates

A new dual-wavelength BH laser emitting at 1.26 and 1.55 µm has been fabricated. The separation between the two active layers is only 2-3 µm, and independent current injection to each active layer is possible. Simultaneous pulsed operation of the two lasers at room temperature and CW operation at -20°C have been achieved.

Kenichiro Takahei

Papers

InP/GaInAsP Buried Heterostructure Lasers of 1.5 µm Region

Effect of Baking Temperature on Purity of LPE Ga0.47In0.53As

Instability of In-Ga-As-P Liquid Solution during Low Temperature LPE of In1-xGaxAs1-yPy on InP

1.5 µm InGaAsP/InP BH Lasers on p-Type InP Substrates

InGaAsP/InP Dual-Wavelength BH Laser