Double Heterostructure Wafers Research Articles

Elastic and plastic contributions to X-ray Line broadening of InGaAsP/InP Heterostructures

The coherency state of MOCVD grown InGaAsP/InP double-heterostructure wafers was examined and their effects on the structural properties were determined in this study. Lattice mismatches were measured using {511} asymmetric and (400) symmetric x-ray reflections. The chemical lattice misfit and the elastic strain were also calculated. Misfit dislocations were examined by both x-ray topography and photoluminescence imaging. The x-ray full width at half maximum (FWHM) varied with the degree of mismatch. The largest FWHM was obtained for samples containing the misfit dislocations. It was found that FWHM is influenced not only by the plastic deformation, but also by the elastic strain. To model the dependence of the FWHM, the radius of curvature was measured, and its contribution to the x-ray line broadening was calculated. Also, the contribution from misfit dislocations was taken into account. This model assumes that the dislocations are planar and interact weakly with each other. Good agreement between measured and calculated values was obtained. Thus, it is concluded that the major contribution to x-ray line broadening ofelastically strained sample is the lattice curvature induced by misfit strain, and that the dominant factor affecting x-ray FWHM ofplastically deformed sample is lattice relaxation induced by misfit dislocation.

Metalorganic vapor phase epitaxical growth and 1.5-μm laser fabrication using ethyldimethylindium, tertiarybutylphosphine, and tertiarybutylarsine

High-quality InGaAsP lattice matched to InP was grown by low-pressure metalorganic vapor phase epitaxy using ethyldimethylindium (EDMIn), tertiarybutylphosphine (TBP), and tertiarybutylarsine (TBA). The background carrier concentrations of undoped InP and InGaAs were as low as 1.5×1015 and 2.2×1015 cm−3, respectively. Good compositional control of In-GaAsP was also possible. The performance of the double heterostructure wafers employed as lasers as characterized by threshold current density, internal loss, and internal quantum efficiency. The threshold current density for a 300-μm cavity was as low as 2.0 kA/cm2. In addition, ridge-waveguide distributed feedback lasers were successfully fabricated. These results show that EDMIn, TBP, and TBA might be used to replace conventional sources for growing InGaAsP/InP lasers.

Growth of Ga0.47In0.53As/InP Double-Heterostructure Wafers by Chemical Beam Epitaxy (CBE)

GaInAs/InP wafers with a thick active layer (0.5-2.0 µm) were grown by chemical beam epitaxy (CBE). Stripe-contact lasers were fabricated to evaluate these wafers. The lowest normalized threshold current density obtained was 7.9 kA/cm2·µm for devices with a 2.0 µm thick active layer. This value is almost acceptable for application to surface emitting lasers.

Observation of the i=1/2 fractional quantum Hall plateau in AlGaAs/GaAs/AlGaAs selectively doped double heterostructures

An inverted and a normal GaAs/AlGaAs interface grown back to back in a socially selectively doped double heterostructure (SDDH) has been studied in magnetic fields up to 12 T and at temperatures down to 0.3 K. The longitudinal resistance goes to zero at the minima of the Shubnikov-de Haas oscillations. The Hall resistivity is found to exhibit the quantum Hall effect. By etching the surface of the double heterostructure wafer the authors create an imbalance in the density of electrons in the two parallel two-dimensional electronic sheets. Although in this way they create only a modest change in the electron densities, they observe a significant change in the Shubnikov-de Haas oscillations, which can be interpreted as a beat between the oscillations of two electron layers with different densities. At the same time they observe a significant variation of the width of the quantum Hall steps. The most astonishing feature of the results is a clear quantum Hall plateau at 1/2 filling in each of the two parallel layers observed at temperatures below 1 K and at a magnetic field about 10 T. Weak localisation was also studied and such experiments are consistent with two parallel and independent two-dimensional electronic layers.

Fabrication of buried-heterostructure diode lasers using i n s i t u Mg diffusion

An in situ diffusion technique is developed to simplify the diode-laser fabrication process. In this technique Mg is diffused into double-heterostructure wafers during their liquid-phase-epitaxial growth process through an in situ formed diffusion mask, which makes separate mask-formation and diffusion processes unnecessary. Buried-heterostructure lasers with low threshold and high efficiency are fabricated utilizing this simplified process.

Characterization of InGaAsP/InP double-heterostructure wafers grown by metalorganic vapor phase epitaxy for semiconductor lasers by photoluminescence investigation with high-power YAG-laser excitation

The photoluminescence (PL) spectrum distribution of a low-pressure metalorganic vapor-phase epitaxy grown wafer with an InGaAsP/InP double heterostructure (DH) was measured under the irradiation of a high-power Nd-YAG laser. The two-dimensional distribution profiles of the PL intensity and peak wavelength in the wafer are discussed in terms of the temperature profile on the substrate surface during growth. A change in the decomposition ratio of the reaction gas due to a temperature change on the substrate surface was found to cause the compositional (PL wavelength) distribution on the wafer and the subsequent lattice mismatch, which is considered to be the main factor influencing PL characteristics. Laser diodes (LDs) were fabricated from the DH wafer, and both PL and LD characteristics were compared. The PL intensity was found to be in reciprocal proportion to the threshold current of the LD, and the PL peak wavelength had a parallel red shift of 10–30 nm to the lasing wavelength. As a result, the LD characteristics, the threshold current, and the lasing wavelength could be predicted from the high-power PL measurements of the as-grown wafer before the LD fabrication processing.

Performance of dry-etched short cavity GaAs/AlGaAs multiquantum-well lasers

Fabrication and lasing characteristics of short cavity GaAs/AlGaAs multiquantum-well (MQW) lasers with dry-etched facets are described in detail. The lasers are fabricated from GaAs/AlGaAs double-heterostructure wafers grown by molecular-beam epitaxy. Fabry–Perot cavities are formed by a reactive ion-beam etching technique with Cl2 plasma. The dependence of lasing characteristics on the cavity length is examined. A threshold current as low as 30 mA is achieved for 20-μm-long cavity MQW lasers with 12 110-Å-thick GaAs wells separated by 11 50-Å-thick Al0.2Ga0.8As barriers. The very short cavity lasers with large mode spacing realize the stable single-longitudinal-mode operation. Furthermore, the lasers show good high-frequency performance. A relaxation oscillation frequency as high as 32 GHz is observed with a 30-μm-long laser. Temperature characteristics are also presented.

GaAs surface emitting lasers with circular buried heterostructure grown by metalorganic chemical vapor deposition and two-dimensional laser array

A metalorganic chemical vapor deposition (MOCVD) was used to grow both double-heterostructure wafers and circular buried heterostructures for GaAlAs/GaAs surface emitting lasers. A vertical microcavity was formed with a diameter of 10 μm and a cavity length of 6 μm by a two-step MOCVD growth and fully monolithic technology. Threshold currents under room-temperature pulsed conditions ranged from 50 to 100 mA with a minimum of 50 mA. cw operation up to 160 K was obtained. In addition, a densely packed 5×5 SE laser array with 20 μm separation was demonstrated with a minimum threshold of 600 mA.

680-nm band GaInP/AlGaInP tapered stripe laser

A gain-guiding tapered stripe laser was fabricated using a Ga0.5In0.5P/(Al0.5Ga0.5)0.5In0.5P double heterostructure wafer grown by metalorganic chemical vapor deposition. The laser showed a continuous wave (cw) threshold current of 48 mA, a maximum temperature for cw operation of 81 °C, an aspect ratio of about 2, and an astigmatism near 25 μm. The emission wavelength was 684 nm. Thirty-two devices have been operating without significant degradation for more than 2000 h at 50 °C with a constant output power of 3 mW.

Influence of phosphorus vapor ambient for InGaAsP growth on GaAs substrate

For visible-light-emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid-phase epitaxy. As the growth temperature is as high as about 780 °C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In-P-Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (λPL=805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x-ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of increasing the flow rate of H2 gas in order to protect the solution for the active layer from phosphorus contamination, the double heterostructure wafers with the high-quality active layer can be obtained reproducibly. Thus, pulsed lasing operation at room temperature has been achieved. The lasing wavelength is 816 nm and the threshold current density is ∼4.6 kA/cm2.

Chemical beam epitaxial growth of very low threshold Ga0.47In0.53As/InP double-heterostructure and multiquantum well lasers

We report the successful preparation by chemical beam epitaxy and performance characteristics of Ga0.47In0.53As/InP double-heterostructure (DH) and multiquantum well (MQW) lasers emitting at 1.47–1.72 μm. The very low threshold current densities Jth of 1.3 kA/cm2 and 1.5 kA/cm2 obtained from DH and MQW laser wafers, respectively, suggest that the present materials and heterointerfaces are superior to those obtained previously by other techniques. In fact, these Jth’s are the lowest obtained thus far for such lasers. Differential quantum efficiency of ∼18% per facet was obtained for both DH and MQW lasers. Furthermore, we were able to show that there was a definite improvement in the threshold-temperature dependence characteristic coefficient T0 from ∼35–45 K for DH laser wafers to ∼65–80 K for MQW laser wafers in contrast to previous experimental results.

Fabrication methods for InGaAsP/GaAs visible laser structure with AlGaAs burying layers grown by liquid-phase epitaxy

Liquid-phase-epitaxial (LPE) growth of AlGaAs layers has been used in fabricating InGaAsP buried heterostructure visible lasers on GaAs substrate. InGaAsP/InGaAsP double heterostructure wafers were grown on the p-type GaAs substrates by means of the melt-back method prior to the LPE growth for eliminating phosphorus contamination. An SiO2 film mask was deposited on the epitaxial wafer surface by the rf sputtering, and photoetched with stripes of 7–10 μm width in the 〈110〉 direction. After etching to the first p-InGaAsP cladding layer with a 3% Br-methanol solution, the second LPE growth of n-AlGaAs and p-GaAs layers was carried out. The InGaAsP active region is entirely surrounded by the InGaAsP cladding layers and the AlGaAs burying layer, therefore, it becomes possible to provide both lateral and vertical carrier and optical confinements. I-L characteristics were measured at room temperature under pulsed operation, but the lasing action was not obtained. The peak wavelength of the electroluminescence was 785 nm. The transverse mode behavior was analyzed by means of the effective refractive index approximation. And it seemed that this buried heterostructure is suitable for the transverse mode control of InGaAsP visible laser diodes.

Room-temperature cw operation of InGaP/InGaAlP visible light laser diodes on GaAs substrates grown by metalorganic chemical vapor deposition

Room-temperature cw operation for InGaP/InGaAlP double heterostructure (DH) laser diodes on GaAs substrates was achieved for the first time. The DH wafers were grown by low-pressure metalorganic chemical vapor deposition using methyl metalorganics. A lasing wavelength of 679 nm and a threshold current of 109 mA at 24 °C were obtained for an inner stripe structure laser diode with a 250-μm-long and 7-μm stripe geometry. The laser operated at up to 51 °C. The characteristic temperature T0 was 87 K at around room temperature. The lowest threshold current density, 5.0 kA/cm2, was obtained with a 20-μm stripe width laser diode under room-temperature pulsed operation.

Room-temperature continuous-wave operation of an AlGaInP double heterostructure laser grown by atmospheric pressure metalorganic chemical vapor deposition

Continuous-wave (cw) operation at temperatures up to 23 °C of an Al0.26Ga0.26In0.48P/Ga0.52In0.48P/ Al0.26Ga0.26In0.48P double heterostructure (DH) laser has been achieved for the first time. The threshold current was 160 mA at 20 °C for a device with a 10-μm-wide and 250-μm-long ion-implanted stripe geometry. The emission wavelength was 671 nm during cw operation at 10 °C. To reduce thermal resistance to a heat sink, a dually stacked structure made of a thin (∼0.3 μm) p-AlGaInP layer and a p-Al0.76Ga0.24As layer was used as a cladding layer. The DH wafer was grown by atmospheric pressure metalorganic chemical vapor deposition.

CW operation at - 10°C for InGaAlP visible light laser diodes grown by MOCVD

CW operation at - 10°C for InGaP/InGaAlP double heterostructure (DH) laser diodes has been achieved for the first time. The DH wafers were grown by low-pressure metalorganic chemical vapour deposition using methyl metalorganics as the source of group III elements. Under room-temperature pulsed operation, the lasing wavelength was 663 nm and the lowest threshold current density was 7.8 kA/cm2. The CW characteristic temperature T0 was 63 K at around -30°C.

1.6 GHz electroabsorption light modulation in InGaAsP/InP double heterostructures with strip-loaded planar waveguide

Low-voltage driving and high-speed modulations of InGaAsP/InP electroabsorption modulators with strip-loaded planar waveguide have been described. The modulators were fabricated from VPE-grown InGaAsP/InP double-heterostructure wafers. For λ=1.55 μm incident light an extinction ratio of 20 dB was achieved with an applied voltage of ∼−6 V. The insertion loss was 9.6 dB. The calibrated 3 dB bandwidth was 1.6 GHz.

Cw operation of an AlGaInP double heterostructure laser diode at 77 K grown by atmospheric metalorganic chemical vapor deposition

Continuous wave operation of an Al0.21Ga0.31In0.48P /Ga0.52In0.48P /Al0.21Ga0.31In0.48P double heterostructure (DH) laser diode was achieved for the first time at 77 K. The device was made from a DH wafer grown by atmospheric metalorganic chemical vapor deposition using triethyl metals and phosphine as source materials. At 77 K, the lasing wavelength was 0.653 μm and the threshold current was 55 mA for a diode with a nitride-insulated, 8-μm-wide and 250-μm-long stripe geometry.

Effect of photocarrier spreading on the photoluminescence of double heterostructure material

Lateral spreading of photoexcited carriers can suppress the photoluminescence signal from double heterostructure wafers containing a p-n junction independently from saturable defects in the material. Experimental results are presented and a theory is derived to show that in any double heterostructure with a p-n junction the photoluminescence is suppressed if the power of the excitation source does not exceed a threshold value. The threshold power has been calculated in terms of material parameters, in excellent agreement with experimental results. This effect is the basis of a novel technique used for a nondestructive optical determination of the p-clad layer sheet conductance as well as junction misplacement in double heterostructures, both of which are important parameters for injection lasers.

Misfit dislocations in (111)A InP/In0.53Ga0.47As/InP double heterostructure wafers grown by liquid phase epitaxy

The behavior of misfit dislocations in (111)A InP/In0.53Ga0.47As/InP double heterostructure (DH) wafers, grown by liquid phase epitaxy, has been investigated by x-ray and photoluminescence (PL) topography and compared with those in (100) and (111) B quaternary DH wafers. Misfit dislocations are generated at wafer edges and are located in close proximity to the heterointerface in the upper InP layers. These dislocations were determined to be the same as in the case of (100) DH wafers. The misfit dislocation free area, as determined by PL topography with Ar+ ion laser excitation, decreases rapidly when the upper InP layer thickness approaches about 1 μm. Nearly misfit dislocation free DH wafers were obtained by a two step growth of the upper InP layer. In (111)A ternary DH wafers, with a lattice mismatch of 0% to −0.03% at room temperature, misfit dislocations are mostly β-type 60° dislocations. These misfit dislocations are not observed by PL topography when ternary layers are excited by a Nd-doped Yttrium Aluminium Garnet (Nd:YAG) laser. Misfit dislocations of the α type, introduced in (111)B quaternary DH wafers with a lattice mismatch of the same sign and magnitude, are clearly observed as dark lines under Nd:YAG laser excitation.

Low threshold GaInAsP/InP buried-heterostructure lasers with a chemically etched and mass-transported mirror

The mass-transport technique has been used to improve chemically etched mirrors on GaInAsP/InP double heterostructure wafers. Vertical and flat mirror facets have been obtained. Buried-heterostructure lasers fabricated with one such mirror and the other mirror cleaved show high device yield with threshold currents as low as 6 mA and differential quantum efficiency as high as 33%.