M. A. Tischler

Controlled carbon doping of GaAs by metalorganic vapor phase epitaxy

The controlled incorporation of carbon has been demonstrated for the metalorganic vapor phase epitaxy of GaAs. Carbon levels between 1016 and 1019 cm−3 can be achieved under typical growth conditions by using Ga(CH3)3 and either As(CH3)3 or mixtures of As(CH3)3 and AsH3. The carbon incorporation into GaAs goes through a minimum with growth temperature at ∼650u2009°C when using Ga(CH3)3 and As(CH3)3. The controlled addition of AsH3 monotonically decreases the carbon incorporation. The high carbon levels (≳1–2×1019 cm−3), greater than the reported solid solubility, are thermally stable with a low diffusion coefficient. The GaAs:C layers exhibit a low deep level concentration, ∼1013 cm−3, with only a single midgap trap present.

Selective epitaxy in the conventional metalorganic vapor phase epitaxy of GaAs

The selective epitaxy of GaAs was demonstrated in the metalorganic vapor phase epitaxy of GaAs utilizing diethylgallium chloride [Ga(C2H5)2Cl] and AsH3. No GaAs will deposit on SiO2, Si3N4, or SiONx under normal growth conditions, i.e., 600–800u2009°C at 0.1 atm reactor pressure. Unlike other forms of selective epitaxy, there is no enhanced growth rate at the edge of the selectively grown regions. The selectivity is a result of the reduced adsorption of the growth precursor, probably GaCl, on the masking material relative to the exposed GaAs areas. Similar selectivity should be possible for Al and In containing semiconductors using an analogous growth chemistry.

The control and modeling of doping profiles and transients in MOVPE growth

Abstract The accurate placement of dopants during chemical vapor deposition is complicated by many factors: growth temperature, reactor design, flow conditions, and the choice of growth and doping chemistry. Long doping transients have often been noted in structures grown using, for example, dopant precursors such as H 2 Se and Mg(C 5 H 5 ) 2 . These transients appear at the “turn-on” of a dopant source as well as the termination or “turn-off” of the source. The grown-in dopant profiles are also modified by the diffusion of the dopant during the thermal history of the structure. The major cause of these transients in the case of metal-organic doping sources, such as Mg(C 5 H 5 ) 2 , is the adsorption and desorption of the dopant precursors on the internal surfaces of the reactor. We have developed a heuristic model of this process which can describe the major features of this process. Growth conditions and dopant source characteristics are described which minimize these growth transients.

GaN Growth by Metallorganic Vapor Phase Epitaxy A Comparison of Modeling and Experimental Measurements

A model for the growth of gallium nitride in a vertical metallorganic vapor phase epitaxy (MOVPE) reactor is presented and compared to experimental growth rate measurements. For a mixture of nondilute gases, the flow, temperature, and concentration profiles are predicted using recent kinetic data. Growth rates are predicted based on simple reaction mechanisms and compared with those obtained experimentally. These comparative results show that the growth of GaN epi layers proceeds through an intermediate adduct of trimethylgallium and ammonia. Loss of adduct species due to oligmerization leads to the lowering of the growth rate. Quantification of this loss of reacting species is made based on experimentally observed growth rates. An apparent chemistry model is presented based on the salient features of GaN MOVPE. Process conditions are perturbed to obtain trends in growth rate and uniformity in order to demonstrate the utility of such a model in optimizing the GaN MOVPE process.

Doping and dopant behavior in (Al,Ga)As grown by metalorganic vapor phase epitaxy

Abstract The controlled doping of n- and p-type Al x Ga 1−x As has been studied for the dopant elements, C, Zn, Si, and Sn. Both the incorporation characteristics and the electrical properties of these dopants are reviewed and discussed fo Al x Ga 1−x As grown by th metal-organic vapor phase epitaxy (MOVPE) technique. The incorporation of Si from SiH 4 and Si 2 H 6 is dominated by heterogeneous and homogenous reactions respectively and represents the best understood of the doping systems. Zinc and carbon both possess complex dependencies on the MOVPE growth system parameters. The electrical behavior of n-Al x Ga 1− x As is dominated by the presence of the DX center. The relationship between this center and the electrical behavior of the material must be understood in order to properly characterize the doping behavior in Al x Ga 1−x As layers and structures.

Determination of epitaxial AlxGa1−xAs composition from x‐ray diffraction measurements

The correlation between the aluminum composition in epitaxial AlxGa1−xAs and double crystal x‐ray diffraction measurements was quantitatively determined. The angular separation ΔΘ, between the diffraction peaks from the AlxGa1−xAs layer grown by metalorganic vapor phase epitaxy and the GaAs substrate increased nonlinearly with the Al content, which was independently determined using photoluminescence and electron microprobe measurements. The calibration curve was used to determine AlAs materials parameters. The AlAs lattice constant and Poisson ratio were determined to be 5.6622 A and 0.275, respectively, assuming that the GaAs parameters are 5.65325 A and 0.311.

Selective epitaxy of GaAs, AlxGa1−xAs, and InxGa1−xAs

Abstract Many device structures benefit from the ability to selectively deposit epitaxial materials. Through the use of a masking material, such as Si3N4 or SiO2, on the substrate surface, patterns generated through standard lithographic procedures can be used to define regions for selective deposition. Highly selective growth can be achieved through the use of growth precursors which contain halogens, such as (C2H5)2GaCl and (C2H5)2AlCl. These compounds decompose, most probably, to the volatile mono-halogen species, e.g. GaCl, and also generate HCl in the gas phase as a reaction by-product. We present experimental results on the morphology and growth behavior of GaAs, AlxGa1−xAs, and InxGa1−xAs using this selective epitaxy technique. Electri cal and optical characterization has been carried out on these materials and selectively grown structures produced by this technique. The interface between the selectively grown material and the underlying substrate was investigated and the conditions for achieving high quality electrical interfaces were determined. A thermodynamic model of this growth chemistry predicts the trends in composition and growth rate. The thermodynamic model, based on the quasi-equilibrium of the halogen-based compounds with the substrate surface, indicates that the growth behavior is very similar to the inorganic-based growth of these compounds. Experimental applications of this technique to high speed digital device structures and sub-micron dimensioned optical structures are presented.

Recent progress in atomic layer epitaxy of III–V compounds

Abstract Atomic layer epitaxy (ALE) has been recently established as a new growth technique which allows control of the growth process at the monolayer level through a self-limiting growth mechanism. We report here on recent progress and current problems facing this technology. Side wall growth by ALE has been demonstrated with deposited structures that differ from conventional chemical vapor deposition growth. Also ALE shows promise in the growth of GaAs on nonpolar substrates such as Ge. The problem of background doping in ALE films will be addressed.

Deep levels in p‐type GaAs grown by metalorganic vapor phase epitaxy

We report a detailed deep level transient spectroscopic study in p‐type Mg‐ and Zn‐doped GaAs epitaxial layers grown by metal‐organic vapor phase epitaxy. Dependence of deep level structures on doping concentrations and growth temperatures has been investigated. Over a wide range of growth conditions, four hole traps and an electron trap ranging in activation energy from 0.18–0.79 eV were measured in GaAs:Mg while only a single hole trap has been observed in GaAs:Zn.The presence of a certain trap and its concentration in GaAs:Mg depends mainly on the doping concentration in the layers. The total trap concentration in the GaAs:Mg decreases rapidly with doping concentration for p>4×1017 cm−3. The physical and chemical origins of several of these traps have been identified. The Mg‐doped GaAs always exhibited a greater concentration of midgap trap levels than the Zn‐doped material, regardless of dopant concentration or growth temperature. The overall defect structure and dopant incorporation characteristics i...

Thermally stable and nonspiking Pd/Sb(Mn) ohmic contact to p‐GaAs

A thermally stable, nonspiking ohmic contact to p‐GaAs has been developed based on the solid‐phase regrowth mechanism. The contact metallization consists of a layered structure of Pd(250 A)/Sb(100 A)/Mn(10 A)/Pd(250 A)/p‐GaAs. Thermal annealing of the contact between 300 and 600u2009°C for 10 s yields contact resistivities in the range of low 10−6 Ω cm2 on substrates doped to 2.5×1018 cm−3. A contact resistivity of 4.5×10−7 Ω cm2 can be obtained after annealing at 500u2009°C on samples with a doping concentration of 4.5×1019 cm−3. The contact metallization remains uniform in thickness and the contact interface is flat after the contact is formed. The consumption of the substrate is limited to less than a hundred angstroms. Contact resistivities are stable at 400u2009°C.