R. Potemski

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 ∼650 °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.

Properties of high‐purity AlxGa1−xAs grown by the metalorganic vapor‐phase‐epitaxy technique using methyl precursors

The metalorganic vapor‐phase epitaxy (MOVPE) of AlxGa1−xAs most commonly employs the methyl precursors Al(CH3)3 and Ga(CH3)3. These precursors were used in the growth of AlxGa1−xAs over the entire range of alloy composition in a low‐pressure horizontal MOVPE reactor. A complete chemical, electrical, and optical characterization of high‐purity MOVPE AlxGa1−xAs grown over the entire range of growth temperatures (600–800 °C) was carried out in order to determine the relationship of the materials properties to the growth conditions. Carbon, the primary impurity in the layers, dominates the electrical properties of the epitaxial layers. A superlinear dependence of carbon incorporation on AlAs mole fraction is observed, along with a two‐slope dependence on growth temperature. Photoluminescence spectra (2 K) were obtained from materials with AlAs mole fraction over the range 0≤x≤0.80. The photoluminescence intensity of the layers also exhibits a systematic dependence on alloy composition and growth temperature. ...

The influence of growth chemistry on the MOVPE growth of GaAs and AlxGa1−xAs layers and heterostructures

Abstract A comparison study was carried out on the influence of the growth chemistry on the properties of Al x Ga 1− x As and GaAs layers and quantum well structures. Triethylgallium, triethylaluminum, trimethylgallium, and trimethylaluminum were used in a various combinations during MOVPE growth of Al x Ga 1− x As. Substantial reductions in the carbon incorporation can be achieved using the ethyl based growth chemistry. The observed change in the carbon incorporation with growth chemistry indicates a change in the decomposition kinetics and mechanisms between the various growth precursors. While triethylgallium can be directly substituted for trimethylgallium in the growth of Al x Ga 1− x As, the use of triethyl aluminum requires particular care. Narrow quantum well structures were demonstrated using both ethyl and methyl based precursors.

Dependence of the AlxGa1−xAs band edge on alloy composition based on the absolute measurement of x

The absolute determination of the Al concentration, x, in epitaxial layers of AlxGa1−xAs was carried out using a nuclear reaction technique. This technique utilizes the narrow resonances found in the 27Al( p,γ)Si28 reaction, together with Rutherford backscattering measurements, to obtain accurate values of the alloy composition. The AlxGa1−xAs band edge was measured on these samples through low‐temperature photoluminescence (2 K) measurements. An improved value of the direct edge (Γ) on composition was determined to be EΓg =1.512 +1.455x(eV) within a ±0.3% limit. The direct‐to‐indirect transition was found to occur at an Al concentration of x≂0.37±0.015, lower than previously reported for He temperatures.

Reduction of background doping in metalorganic vapor phase epitaxy of GaAs using triethylgallium at low reactor pressures

The mechanism of background impurity incorporation in the metalorganic vapor phase epitaxy of GaAs using triethylgallium and arsine was investigated over a wide range of growth parameters. The growth temperature, total reactor pressure, AsH3/Ga(C2H5)3 ratio, and the linear gas velocity were altered in order to ascertain the primary determinants of the background impurity incorporation in the ethyl based chemistry. The GaAs electrical and optical properties are, in general, independent of AsH3/Ga(C2H5)3 ratio but strongly dependent on growth temperature and reactor pressure. Reductions in the reactor pressure, at a constant mass flow rate, result in a linear decrease in the unintentional impurity incorporation, while not changing the growth rate. Substantial improvements in the layer purity with greatly reduced AsH3 consumption can be achieved. A general model of impurity incorporation which relates the effect of reactor pressure and impurity incorporation is presented.

Simulation of Carbon Doping of GaAs During MOVPE

Abstract We present a kinetic model for carbon incorporation during metalorganic vapor phase epitaxy (MOVPE) of GaAs, using trimethylgallium (TMG) and either arsine (AsH 3 ) or trimethylarsenic (TMAs) as growth precursors. The proposed mechanism for the TMG-TMAs-AsH 3 -H 2 system involves 20 gas phase species, 23 gas phase reactions, 14 surface species and 64 surface reactions. The proposed carbon incorporation mechanism is based on the surface formation of Ga-carbene species leading to carbon placement on the arsenic lattice position as observed experimentally. The kinetic mechanism is implemented in a simple reactor model to allow investigations of the reaction pathways without additional complications arising from simulation of complex transport phenomena. The reaction mechanism reflects reported decomposition data for the reactants. Model predictions of carbon concentration levels are in good agreement with published trends in carbon incorporation levels with temperature and the V/III ratio. In particular, the model predicts high carbon incorporation rates when using TMAs and a reduction in carbon concentration levels as AsH 3 is added to the reaction mixture in increasing amounts.

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., 600–800 °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.

Quantitative oxygen measurements in OMPVE Al x Ga 1- x as grown by methyl precursors

Oxygen has always been considered to be a major contaminant in the organo-metallic vapor phase epitaxy (OMVPE) of AlxGa1−xAs. Oxygen incorporation has been invoked as a contributor to low luminescence efficiency, dopant compensation and degradation of surface morphology among other deleterious effects. This study presents quantitative measurements of oxygen concentration in nominally high purity AlxGa1−xAs. The oxygen concentration was measured as a function of alloy composition, growth temperature, andV/III ratio. Quantitative secondary ion mass spectroscopy (SIMS) measurements were used to determine the oxygen content as well as the carbon concentration in the film. The oxygen concentration increases with decreased growth temperature and V/III ratio while increasing superlinearly with Al content in the epitaxial layer.

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.

Characterization of epitaxial GaAs and AlxGa1−xAs layers doped with oxygen

Intentional oxygen doping (≳1017 cm−3) of GaAs and Al0.30Ga0.70As epitaxial layers was achieved during metalorganic vapor phase epitaxy through use of an oxygen‐bearing metalorganic precursor, dimethylaluminum methoxide (CH3)2AlOCH3. The incorporation of oxygen and very low levels of Al (AlAs mole fraction <0.005) in the GaAs layers leads to the compensation of intentionally introduced Si donors. Additionally, deep levels in GaAs associated with oxygen were detected. The introduction of dimethyl aluminum methoxide during AlxGa1−xAs growth did not alter Al mode fraction or degrade the crystallinity of the ternary layers, but did incorporate high levels of oxygen which compensated Si donors. The compensation in both GaAs and Al0.30Ga0.70As indicates that high resistivity buffer layers can be grown by oxygen doping during metalorganic vapor phase epitaxy.