T. F. Kuech, D. J. Wolford, E. Veuhoff, V. Deline, P. M. Mooney, R. Potemski, and J. Bradley Citation: Journal of Applied Physics 62, 632 (1987); doi: 10.1063/1.339792 View online: http://dx.doi.org/10.1063/1.339792 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/62/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Very high carbon doping concentration in Al x Ga1x As grown by metalorganic vapor phase epitaxy usingtrimethylaluminum as a doping precursor J. Appl. Phys. 79, 3554 (1996); 10.1063/1.361377 Radiatively controlled lifetimes in Al x Ga1x As grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 64, 1561 (1994); 10.1063/1.111865 Excitonic photoluminescence spectra of Al x Ga1x As grown by metalorganic vapor phase epitaxy Appl. Phys. Lett. 58, 1274 (1991); 10.1063/1.104334 High quality Al x Ga1x As grown by organometallic vapor phase epitaxy using trimethylamine alane as thealuminum precursor Appl. Phys. Lett. 58, 77 (1991); 10.1063/1.104450 Midgap states in metalorganic vapor phase epitaxy grown Al x Ga1 x As J. Appl. Phys. 68, 3394 (1990); 10.1063/1.346344

We present a novel modified technique of in situ etching with tertiarybutyl chloride (TBCl) which allows etching of both, GaInAsP/InP and AlGaInAs/InP structures for the fabrication of buried heterostructure (BH) lasers in an MOVPE system. It is shown that the surface morphology is improved, when small amounts of trimethyl gallium are injected during TBCl etching at reduced reactor pressure. The etching process is performed in a PH3-free atmosphere under hydrogen. Therefore, the etching temperature has to be kept at the relatively low value of 580°C. GaInAsP and AlGaInAs MQW laser ridges can be formed by in situ etching under identical reactor conditions (pressure, temperature, precursor flow). For Al containing layers, however, an ex situ wet chemical etch dip is additionally required in order to avoid residue deposition which results in deteriorated surface morphology. High-quality GaInAsP and AlGaInAs ridges for BH laser applications are obtained. GaInAsP/InP BH lasers fabricated by this technique exhibit excellent high-temperature characteristics.

Tertiarybutylchloride (TBCl) was used for etching of InP based buried heterostructure (BH) laser ridges in an MOVPE system. Applying this in-situ technique with subsequent regrowth will increase process yield and reliability. Etch rates are directly proportional to the TBCl flow. Increasing the hydrogen carrier gas flow yields decreased etch rates, these can be increased at higher temperatures. An excellent surface morphology is essential. This can be obtained under conditions favoring a high surface diffusion. It was found that a PH3-free etching process at 580 degreesC leads to best results both, for InP and GaInAsP layers. An increasing Ga content decreases the etch rate, especially in a PH3-free process. Smooth {111} planes are formed during TBCl etching under optimized conditions. For the first time this process was successfully utilized to produce BH lasers. Device data along with reliability data are comparable with data from devices fabricated by the conventional ex-situ etching process.

Epitaxial growth of InP based strained MQW laser structures is studied for metalorganic vapor phase epitaxy (MOVPE) and metalorganic molecular beam epitaxy (MOMBE or CBE-chemical beam epitaxy). For a tensile barrier layer strain of |/spl epsiv//sub B/|/spl ges/0.4% both in MOVPE and MOMBE, wavy MQW interfaces are observed in TEM along with a severe drop in photoluminescence (PL) intensity and an increase in PL FWHM (full width at half maximum) yielding a significant increase in threshold current density of broad area test lasers. Lateral thickness modulations appear to be much larger in MOVPE than in MOMBE. The V/III ratio appears to be a key parameter for the rate of wavy interface development, which is probably a consequence of surface selective growth. Flat interfaces require low V/III ratios, especially at high strain in the barrier layers resulting in a significant improvement in threshold current density.

The growth parameter dependence of the transition from 2D to 3D growth of GaInAsP multiple quantum well (MQW) structures up to εB=0.5% tensile-strained barriers was examined. Identical MQW structures with εW=1% compressively strained wells were grown by metal organic vapor-phase epitaxy (MOVPE) and metal organic molecular beam epitaxy (MOMBE) and characterized by photoluminescence (PL), X-ray diffraction and transmission electron microscopy. Increasing the tensile barrier strain resulted in deteriorated optical and crystalline properties beyond a critical strain limit, which depends on growth temperature. The deterioration originates from lateral layer thickness and strain modulations. Their density, amplitude and thus their effect on the optical MQW properties are different for both growth methods. High-quality MOMBE-grown MQW structures up to εW=2% compressive well strain and εB=0.5–1% tensile barrier strain could be achieved by inserting thin intermediate layers at each internal interface. The composition of these intermediate layers has a significant effect on MQW material properties.

The doping of InP using Si and Zn has been studied for MOMBE growth on (1 0 0), (1 1 1)A, (1 1 1)B and for the overgrowth of nonplanar surfaces. The investigation of large area growth shows that Si acts as a donor on the three investigated surfaces. The free electron concentrations are always highest on (1 1 1)B and lowest on (1 1 1)A. Zn doping yields free hole concentrations which are highest on (1 1 1)A and lowest on (1 1 1)B. Consequently, co-doping using Si together with Zn yields a net n-type carrier concentration on (1 0 0) and (1 1 1)B surfaces, whereas a net p-type behaviour is found on (1 1 1)A surfaces within the same growth run. These results obtained from large area growth can be transferred to the overgrowth of localized (1 0 0)/(1 1 1)A steps on nonplanar substrates; using Si as dopant the free electron concentration on the (1 1 1)A facet decreases by a factor two compared with the (1 0 0) surface. Si–Zn co-doping leads to a drop in carrier concentration of at least one order of magnitude. Comparison with large area growth suggests that a lateral (p–n)-junction can be realized within a single growth step.

In this study we investigated the material incorporation efficiencies in GaInAsP and InAsP layers grown on InP substrates for large area metalorganic molecular-beam epitaxy (MOMBE). We found an optimum growth temperature for the quaternary material (lambda(G) = 1.55 mu m) around 500-510 degrees C, since in this range the lattice matching shows a temperature coefficient of about 80-120 ppm only. The P incorporation efficiency is improved with increasing growth temperatures (480-520 degrees C). We found for InAsP and GaInAsP (lambda(G) = 1.05 mu m) a strong reduction of the P incorporation efficiency with increasing V/III ratio, which is accompanied by a reduced P content in the layer. Additionally with this reduced P, the Ga incorporation efficiency for the quaternary material is improved. Using the same V/III and As/P ratio for the InAsP and GaInAsP material, a higher P content in the InAsP layers is achieved. The results were used as calibration data for the development of a novel type of wafer holder with improved temperature uniformity. For GaInAsP single layers (lambda G = 1.55 mu m) a standard deviation in emission wavelength of /Delta lambda/ < 1.5 nm was achieved. From the results for all material compositions a temperature distribution with Delta T < 1 degrees C can be inferred across a 2 " wafer. (C) 1998 Elsevier Science B.V. All rights reserved.

Metalorganic molecular beam epitaxy (MOMBE/CBE), which has initially been introduced as a method for fundamental research, has become a growth technology for high quality device structures. The potential of this new technology as an industrial tool for the production of InP based photonic devices is discussed in comparison to metalorganic vapor phase epitaxy (MOVPE). Economical, ecological, yield and safety aspects show a significant advantage of MOMBE for industrial use. Furthermore, the unique MOMBE growth capabilities may open the path to the production of new device generations. Very high volume applications, however, will probably remain the domain of MOVPE. Thus the main industrial application of MOMBE will be in areas where an enabling technology for the production of sophisticated III–V device structures is required. In addition, MOMBE offers advantages, when environmental issues are of major concern, and when stringent safety and yield requirements have to be fulfilled.

Surface selective growth (SSG) is gaining importance for the realization of complex device concepts. This review article addresses basic SSG mechanisms both in metalorganic vapor phase epitaxy (MOVPE) and in metalorganic molecular beam epitaxy (MOMBE/CBE). It is described how these mechanisms can be exploited for the fabrication of complex devices focusing on the InP based material system. Additionally it is shown that with novel precursors new effects can be observed in SSG. The applications of SSG are highlighted by a discussion on selected devices. A critical comparison reveals that SSG in MOVPE can find some applications, but MOMBE offers higher flexibility, moreover a higher yield than in MOVPE can be expected. Therefore, MOMBE appears to be the preferred technology for SSG. However, since MOMBE is not established in production, a substantial R&D back-up is required for an industrial application of SSG in MOMBE.

For applications in long wavelength MQW lasers, GaInAsP/InP heterostructures were grown by metalorganic molecular beam epitaxy (MOMBE or CBE). The growth process was performed with all gaseous sources for group III, group V and dopant precursors. In addition to the standard strained MQW laser structure with two quaternary separate confinement layers on each side of the active MQW region, laser structures with continuously graded GaInAsP confinement layers (GRINSCH) were prepared. In the latter case all group III and group V flows were ramped synchronously while maintaining lattice matching growth conditions. By this method a parabolic variation of the band gap was obtained. Data from first test lasers are comparable to those from standard lasers revealing the high material quality of MOMBE grown InP-based GRINSCH structures. Besides standard strained quaternary layers InAsP layers with compressive strain up to 2% were used as quantum wells, and InAsP MQW lasers with emission wavelengths of both 1.3 and 1.55μm were fabricated. Moreover, an excellent MQW wavelength uniformity (standard deviation Δλ⩽2nm) across areas larger than 95% of a 2″ wafer along with proven thermal stability demonstrates the high yield of the process for all structures revealing the feasibility of this material for industrial use.

For industrial device fabrication gaseous dopant sources are preferred in metalorganic growth technologies. Both in metalorganic vapor phase epitaxy (MOVPE) and metalorganic molecular beam epitaxy (MOMBE/CBE) diethylzinc is used. For doping of InP based ridge waveguide laser structures the critical parts are the active region with GaInAsP confinement layers, MQW layers and the p-type region with InP spacer layer, GaInAsP etch stop layer and InP cladding layer. Growing Zn doped InP in between GaInAsP layers leads to a significant Zn diffusion into the adjacent GaInAsP layers. This effect is much more pronounced in MOMBE than in MOVPE. It is demonstrated how this effect is reduced by insertion of additional intermediate layers with appropriate dopant concentration, and by compensating Si co-doping in the spacer and adjacent layers taking advantage of the Fermi level effect. Applying these techniques, reduced threshold current densities and improved high temperature performance can be obtained. The results are discussed by models of dopant diffusion in MOMBE in comparison to MOVPE, (C) 1998 Elsevier Science B.V. All rights reserved.

In a comparative study we have chosen TBAs and TBP as well as AsH3 and PH3 for the growth of InPGaInAs(P) heterostructures for laser applications in a production metalorganic molecular beam epitaxy (MOMBE) system. The n-type doping was performed with Si from an effusion cell, whereas for the p-type doping Be and DEZn were utilized. InP layers using TBP under optimized cracking conditions exhibit excellent surface morphology with good electrical properties in the low 1015 cm−3 range of carrier concentrations. The MOMBE growth mechanism is not disturbed by the hydride replacement compound. This allows for a convenient replacement without losing calibration data from the hydride process. Broad-area DH laserstructures with GaInAsP (λ = 1.55 μm) active regions were grown with AsH3PH3 and TBAsTBP. Comparable threshold current densities in the range of 1.6-2.3 kA/cm2 are achieved for the lasers, grown with both sets of precursors combined with DEZn source doping. These results are in good agreement with the standard set by the hydride MOVPE process.

The feasibility of metalorganic molecular beam epitaxy (MOMBE or CBE) as a production process is studied with respect to flexibility, uniformity, long term stability and device quality. Gaseous doping sources were used for growth of GaInAsPInP device structures: For n and p type doping disilane and diethylzinc (DEZn), respectively, were injected. The importance of precracking for efficient dopant incorporation is described. For uniform growth across larger areas the dependence of layer composition on growth temperature is critical. Therefore this effect along with the effect of VIII ratio have been studied in detail, and the optimum growth conditions are discussed. It is demonstrated that composition uniformity and long term stability can be obtained leading to variations of emission wavelength and lattice mismatch below ± 1.5 nm and ±1.5 × 10−4, respectively. These material properties are found across an area of about 90% of a 2 in wafer revealing the high yield of this process. As a device test vehicle, strained layer MQW laser structures were grown, and data on broad area threshold current densities are compared with state of the art results from structures grown by metalorganic vapour phase epitaxy (MOVPE).

Diethylzinc was used as a gaseous p-type dopant source for growth of InPGaInAsP layers in metalorganic molecular beam epitaxy. In InP layers a significant effect of growth temperature on Zn incorporation and on electrical activation has been found. Additionally, data from a variation of the dopant cracker cell temperature suggest that the dopant molecules should not be fully decomposed for an efficient dopant incorporation. A comparison of Hall data with data from secondary ion mass spectrometry (SIMS) reveals that in InP up to 60% of the acceptors appear to be electrically active under optimized experimental parameters, in GaInAs the activation is above 90%. The SIMS data show that dopant profiles with steep flanks can be obtained in InPGaInAsP structures. However, a dopant redistribution occurs, which is more pronounced in InP layers. This effect is correlated with the dopant incorporation behaviour on substitutional and interstitial sites. The dopant incorporation process is discussed in detail, and the implications for growth of InPGaInAsP device structures are outlined.

For the fabrication of advanced optoelectronic devices metalorganic growth technologies will play an important role in the next years: metalorganic molecular beam epitaxy (MOMBE) and metalorganic vapor phase epitaxy (MOVPE). Both technologies are basically comparable. The former technology, however, uses a much lower system pressure so that a carrier gas is not required for the growth process. In this case due to the molecular nature of the gas beams gas phase reactions can be excluded. In MOMBE the chemical reactions for crystal growth take place at the growth front leading to surface selective growth (SSG). The mass transfer of reactants to the surface is not affected by desorption from masked or different surface areas so that high perfection selective area epitaxy (SAE) can be achieved. In MOVPE, however, additionally to surface reactions, effects of gas phase reactions and gas phase interdiffusion have to be taken into account

Minimum threshold current density of 0.57kA/cm2 and high T0 values up to 74K were obtained from 400mum long broad area lasers with MOVPE grown compressively strained all-quaternary GaInAsP SCH-MQW layer structures for 1.53mum emission wavelength. With 3mumx400mum RW laserdiodes (T0>90K) high-temperature CW operation up to 130-degrees-C was achieved.