M. Geva

Excimer laser‐induced deposition of InP: Crystallographic and mechanistic studies

InP thin films have been deposited on several types of substrates via 193‐nm excimer laser‐induced photochemical decomposition of (CH3)3In and P(CH3)3 gas‐phase precursors. The characteristics of the deposited films are studied over a wide range of conditions. A photochemical model is proposed which explains the stoichiometry and rate at which the film deposits. Approximate fluences are given for the onset of (in order of increasing fluence) In‐precursor photochemistry, P‐precursor photochemistry, CHx photochemistry, laser‐induced crystallization, and laser damage. Crystallinity of InP films deposited on (100) InP substrates has been studied by scanning electron microscopy, transmission electron microscopy, and Rutherford backscattering spectroscopy. Films range from amorphous to epitaxial, depending upon conditions (most notably fluence incident on the substrate). The best film deposited at ∼0.1 J/cm2 and at a steady‐state temperature of only ∼320 °C had a backscattering spectrum indistinguishable from t...

Excimer laser induced deposition of InP and indium‐oxide films

InP and In‐oxide films have been deposited on quartz, GaAs, and InP substrates by excimer laser induced photodecomposition of (CH3)3InP(CH3)3 and P(CH3)3 vapors at 193 nm. The oxide film refractive index and stoichiometry are close to In2O3. Phosphorus incorporation in the films was greatly enhanced by focusing the laser beam to promote multiple‐photon dissociation processes. These conditions also lead to enhanced carbon inclusion in the films, due to formation of species such as CH and CH2 in the gas phase. However, this carbon inclusion could be suppressed by focusing the beam onto the surface at normal incidence. In the irradiated zone InP could be deposited with P(CH3)3‐to‐(CH3)3InP(CH3)3 ratios of only ∼1:1. The technique offers several potential advantages over conventional metalorganic chemical vapor deposition, including lower temperature, enhanced rates, safer gases, and three‐dimensional film composition control. Strong atomic In emission is observed in the gas phase above the depositing film, d...

Properties of titanium nitride thin films deposited by rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor‐deposition technique using tetrakis (dimethylamido) titanium precursor

Titanium nitride (TiNx) thin films were deposited onto InP by means of the rapid‐thermal‐low‐pressure‐chemical‐vapor‐deposition (RT‐LPMOCVD) technique, using the tetrakis (dimethylamido) titanium (Ti(NMe2)4 or DMATi) complex as the precursor. Depositions were successfully carried out at temperatures below 550 °C, pressure range of 5–20 Torr and duration of 50 to 90 s, to give layer thicknesses up to 200 nm and growth rates in the range of 0.8 to 4.5 nm/s. These films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but also contained a significant amount of carbon and oxygen. The elements were spread uniformly through the films, the nitrogen was Ti bounded, and the carbon was partially titanium bonded and organic bonded as well. The film resistivity was in the range of 400–800 μΩ cm−2; the stress was always compressive, in the range of − 0.5 × 109 to − 2 × 1010 dyne cm−2, and the film had a good morphology. These layers performed as an ohmic contact while depos...

Interface disorder in AlAs/(Al)GaAs Bragg reflectors

We have investigated the structural properties of Bragg reflectors grown by molecular beam epitaxy. The reflectors consist of quarter‐wavelength stacks of AlAs/ AlxGa1−xAs. We find a strong dependence of the interface quality on the substrate growth temperature, the Al composition in the ternary alloy, and the presence of impurities in AlAs. We have classified the interface disorder into two categories: interface roughness and structural waviness. We ascribe interface roughness to the segregation of oxygen during AlAs growth. The structural waviness originates from differing surface migration kinetics of Al and Ga which results in phase separation during growth of AlGaAs.

Growth and fabrication of high-performance 980-nm strained InGaAs quantum-well lasers for erbium-doped fiber amplifiers

A 980-nm strained InGaAs quantum-well (QW) laser is the preferred pump source for an Er/sup 3+/-doped fiber amplifier for the next generation of lightwave communication systems because of lower noise, high power conversion efficiency, and low temperature sensitivity. Obtaining long lifetime, narrow far field, high power output in the fundamental transverse mode centered at 980/spl plusmn/5 nm, and planarity of the structure while maintaining low threshold current density (J/sub th/) and high differential quantum efficiency (/spl eta/) are the major challenges. Here, we report our work aimed at optimizing the design, growth, and fabrication of 980-nm lasers to address some of these issues. We demonstrate very low broad-area J/sub th/, of 47 A/spl middot/cm/sup -2/, operation up to 200/spl deg/C, and a very low linewidth enhancement factor of 0.54 of these lasers. We have also monolithically integrated 980-nm lasers with 850-nm GaAs QW lasers. To minimize coincorporation of nonradiative recombination impurities like oxygen and displacement of the p/n junction due to Be diffusion during MBE growth, we suggest that the Be doping should be dispensed with on the p-side of the GRIN region and the n-side GRIN region should be doped with Si. The optical properties of InGaAs QWs are insensitive to the type of the arsenic beam used, As/sub 2/ versus As/sub 4/. Although strained InGaAs QW lasers grown using As/sub 2/ at a constant substrate temperature as low as 570/spl deg/C have a lower J/sub th/, they also exhibit a 10-25% lower /spl eta/ as compared to the As/sub 4/. counterpart in which the AlGaAs cladding layers are grown at /spl sim/700/spl deg/C. To obtain a planar structure and to prevent the fabrication related defects, we have used a novel method in which the laser structure is first grown by MBE, and mesas are formed by in situ melt etching using SiO/sub 2/ stripes as a mask followed by regrowth of p/sup -/-p-n AlGaAs isolating layers by LPE. Compared to ridge waveguide (RWG) lasers, the buried heterostructure lasers so fabricated have significantly lower threshold current, higher power output; higher temperature operation, lower cavity losses, and kink-free light-current (L-I) characteristics, as expected. A CW power of 150 mW/facet at 986 nm was measured from a 400-/spl mu/m-long BH laser with 11-/spl mu/m active stripe width. A minimum threshold current of 2.5 mA was measured for lasers with 3.0-/spl mu/m active width and 300-400 /spl mu/m cavity length. The L-I characteristics of 500-, 800-, and 1300-/spl mu/m-long lasers with 3.0-/spl mu/m active width were linear up to the currents corresponding to a current density of 10 kA/spl middot/cm/sup -2/. At higher current densities, a sublinear increase of power with current was observed. Stable fundamental transverse mode operation was obtained up to 100-mW emitted power. >

The influence of ammonia on rapid‐thermal low‐pressure metalorganic chemical vapor deposited TiNx films from tetrakis (dimethylamido) titanium precursor onto InP

The process kinetics, chemical composition, morphology, microstructures, and stress of rapid‐thermal low pressure metalorganic chemical vapor deposited (RT‐LPMOCVD) TiNx films on InP, using a combined reactive chemistry of ammonia (NH3) gas and tetrakis (dimethylamido) titanium (DMATi) liquid precursors, were studied. Enhanced deposition rates of 1–3 nm s−1 at total chamber pressures in the range of 3–10 Torr and temperatures of 300 °C–350 °C at a NH3:DMATi flow rate ratio of 1:8 to 1:15 were achieved. Stoichiometric film compositions were obtained, with carbon and oxygen impurity concentrations as low as 5%. Transmission electron microscopy analysis identified the deposited films as TiN with some epitaxial relationship to the underlying (001) InP substrate. This process provides a superior film to the preview RT‐LPMOCVD TiNx film deposited using only the DMATi precursor.

Effects of substrate misorientation on incorporation of ambient oxygen and interfacial roughness in AlGaAs/GaAs heterostructures grown by molecular‐beam epitaxy

By secondary ion‐mass spectrometry (SIMS) and transmission‐electron microscopy (TEM), we have studied the effects of substrate misorientation and GaAs monolayers on the incorporation of ambient oxygen and interfacial roughness in AlxGa1−xAs/GaAs heterostructures grown by molecular‐beam epitaxy. Consistent with earlier works, O is found in AlGaAs only, and not in GaAs. Incorporation of O, and surface and interfacial roughness are reduced if the substrate is misoriented towards 〈111〉A. The O atoms in AlGaAs are mobile enough to segregate on the surface and remain trapped at the GaAs/AlGaAs inverted interfaces, even when the GaAs layer is as thin as one monolayer.

CONCENTRATION DEPENDENT ZN DIFFUSION IN INP DURING METALORGANIC VAPOR PHASE EPITAXY

Concentration dependent diffusion of Zn during metalorganic vapor phase epitaxy from a Zn‐doped InP layer into the adjacent undoped InP buffer layer were studied systematically using secondary ion mass spectroscopy and carrier concentration profiling. Under the condition that the growth rate of the Zn‐doped film is faster than the interdiffusion of Zn into the underlying undoped buffer layer, the diffusion problem can be treated as a one‐dimensional diffusion couple between two semi‐infinite media. Furthermore, Zn diffusion during the optimized growth condition for InP completely eliminates the thermal decomposition problem encountered in the sealed ampoule and open tube diffusions and also maintains all the intrinsic point defects at their thermodynamic equilibrium concentrations. With an optimal growth temperature at 625 °C and a maximum Zn flow below the incorporation limit for substitutional Zn to ensure that the dominant Zn are incorporated substitutionally, the diffusion profiles of Zn across the in...

Residual oxygen levels in AlGaAs/GaAs quantum‐well laser structures: Effects of Si and Be doping and substrate misorientation

Oxygen forms nonradiative recombination centers in GaAs and AlGaAs, and is a common contaminant in AlGaAs, irrespective of the growth technique. We find that O tends to accumulate near the GaAs active region of an AlGaAs/GaAs quantum‐well laser prepared by molecular beam epitaxy. Moreover, the Be‐doped Al0.6Ga0.4As cladding layer has a higher O content than its Si‐doped counterpart. We present evidence that Si‐doping suppresses, and Be doping favors incorporation of O in AlGaAs. In undoped and Si‐doped AlGaAs, the incorporation of O is further reduced by tilting the (100) GaAs substrates towards 〈111〉A. We propose that Be forms stable Be‐O complexes in AlGaAs, and thus, there is virtually no desorption of incorporated O. But in Si‐doped AlGaAs, O content is reduced due to reaction between group III suboxides and Si, resulting in the formation and desorption of volatile SiO (g). The study suggests that Be doping should be avoided in the p‐side of the GRIN region of a laser structure.

Direct evidence for the role of gold migration in the formation of dark‐spot defects in 1.3‐μm InP/InGaAsP light‐emitting diodes

The results of our previous study of dark‐spot defects (DSD’s) in aged 1.3‐μm InP/InGaAsP light‐emitting diodes (LED’s) have strongly suggested that the defects form as a result of the migration of gold from the p contact into various epitaxial layers. To provide further support for this degradation mechanism, we compare, in this study, the formation of DSD’s in LED’s fabricated with the usual BeAu p metallization and a new platinum p contact. After accelerated aging (200 °C junction temperature, 20 kA/cm2, 3×103 h), DSD’s were observed only in the devices with BeAu contacts, thus directly identifying the active role of gold migration in DSD formation.