Richard A. Morrow

Modeling the diffusion of hydrogen in GaAs

Concentration depth profiles of carriers (or of electrically active defects) and/or deuterium in GaAs following exposure to a hydrogen plasma (or, in one case, to molecular hydrogen) are fit using a simple diffusion model with second‐order reactions. We find that (1) the activation energy for hydrogen diffusion and the dissociation energies of hydrogen‐defect complexes are dependent on the concentration of hydrogen, (2) there is no molecular hydrogen formation and no fast‐diffusing species of hydrogen away from the near‐surface region, and (3) atomic hydrogen can in‐diffuse and passivate EL2 defects when semi‐insulating GaAs is annealed at a high temperature in a molecular hydrogen ambient.

Model of EL2 formation in GaAs

It is demonstrated that existing thermodynamic data on the native deep donor, EL2, in melt‐grown and epitaxially grown GaAs are consistent with that defect having the atomic structure AsGaVGa. In melt‐grown GaAs at high temperatures (∼1200 °C) arsenic antisite defects appear as the complex AsGaVAsVGa. As the temperature drops toward 1000 °C and the equilibrium concentration of divacancies decreases this complex dissociates, the divacancies outdiffusing and the antisites capturing gallium vacancies to form EL2. In GaAs grown by organometallic vapor‐phase epitaxy it is suggested that the arsenic interstitial is the dominant native defect produced in equilibrium with the vapor and that it dictates the deviation from stoichiometry of the epilayer. Below the growth interface these interstitials rapidly react with indiffusing divacancies to form primarily arsenic antisites. Other divacancies then react with the antisites to briefly form the complexes AsGaVAsVGa which, in the nonuniform temperature regime of the...

Electrical activation of silicon coimplanted with nitrogen, phosphorus, or arsenic in semi‐insulating GaAs substrates grown by the liquid encapsulated Czochralski method

We fit some existing data on the electrical activation of Si ions coimplanted with either N, P, or As ions in semi‐insulating GaAs substrates grown by the liquid encapsulated Czochralski method. For one data set the activation anneal was done with proximity capped samples in a flowing H2 ambient, and for the other data sets anneals were done with dielectric capped samples. We are able to obtain good fits to all data with simple choices for the depth profiles of implanted ions if we adopt the following assumptions: (1) With no group V coimplants, the Si donors formed during a dielectric cap anneal, possibly SiGaVAs, are 100% ionized, while some of those formed during a proximity cap anneal in H2, possibly SiGaHAs, are less than 100% ionized and also serve to eliminate some arsenic vacancies. (2) All Si‐related acceptors appear as BGaSiAs defects. (3) The observed enhancement of Si activation with coimplanted P is due to a decreased concentration of BGaSiAs acceptors whose formation is inhibited by P. (4) C...

Stoichiometric structures of defects in high-purity GaAs grown by the liquid encapsulated Czochralski method

We analyze some existing data obtained on a GaAs sample grown by the liquid encapsulated Czochralski (LEC) method from a near‐stoichiometric melt after the sample was cycled through various thermal processes. By using the constraint of constant deviation from stoichiometry we are led to suggest that the defects observed or inferred to exist in the sample have the following properties: (1) the acceptor associated with the 1.45‐eV photoluminescence signal has the stoichiometric structure of GaAs if doubly charged or of VGaGaAs if singly charged; (2) the (presumed) donor at Ec−0.134 eV has the stoichiometric structure of VAs; (3) another (inferred) acceptor has the stoichiometric structure of VGa; and (4) the very shallow donor at Ec−0.003 eV is the precursor of EL2 and becomes EL2 upon reaction with VGa or its stoichiometric equivalent.

Silicon donor‐hydrogen complex in GaAs: A deep donor?

Post‐hydrogenation anneals of shallow SiGa donors in GaAs indicate that their reactivation rate is enhanced in the presence of an applied electric field. We show that existing data are consistent with the SiGa‐H complex being a deep donor dissociating only via its ionized state. The 0/+ level of this deep donor is found to be at EC−0.75 eV. There is no need to appeal to the existence of negatively charged hydrogen to account for the reactivation of SiGa donors.

Kinetics of formation and dissociation of a dominant native defect (EL2) in GaAs

It is shown that a simple kinetic model can account for existing data both on the formation of the native defect EL2 in the temperature range 644–800 °C in GaAs samples from which EL2 was eliminated by a 1200 °C anneal/quench and on the disappearance of EL2 during anneals in the temperature range 1000–1200 °C. Our analysis suggests that EL2 consists of VGa bound to an unidentified ‘‘kernel’’ which, if not actually stable at temperatures up to 1200 °C, forms relatively rapidly at the lower temperatures and dictates the final concentration of EL2 in the sample. The change in enthalpy involved in the capture or release of VGa by the kernel is estimated to be 5.6 eV.

Diffusion in GaAs of a native defect tagged with deuterium

We interpret published depth profiles of deuterium in n‐ and p‐type GaAs, following long anneals at 500 °C in a gaseous deuterium atmosphere, as indicating the indiffusion of a native defect (probably VAs) and an impurity (possibly O), both tagged with deuterium. Model fits yield the 500 °C diffusivity of the tagged impurity as 4×10−14 cm2/s and the diffusivities of the tagged native defect as 3×10−15 cm2/s in n‐GaAs and ∼8×10−15 cm2/s in p‐GaAs.

Theory of EL2 and EL5 formation in melt‐grown GaAs:Si

Reactions conjectured to occur during the cooldown of GaAs grown from the melt are presented. These are used to fit existing data on the dependence of various concentrations (carrier, EL2, and EL5) on melt composition in crystals grown from a Ga‐rich melt doped with silicon. Acceptable fits are based on the following model assumptions: (1) EL2 is AsGaVGa, (2) EL5 is the acceptor complex SiGaVGa, and (3) freeze‐out of the reaction VGa+AsGaVAs=AsGaVAsVGa during cooldown is responsible for a large VGa concentration and a concomitant restricted EL2 concentration in the crystal.

Electrical activation curve of silicon implanted in GaAs

A model describing the electrical activation of silicon implanted in semi‐insulating GaAs is fit to carrier concentration versus silicon concentration data spanning over three decades. The model incorporates the reactions of silicon with boron and EL2 present in the substrate.

Defect formation in GaAs grown by organometallic vapor phase epitaxy and the structure of the native defect EL2

Abstract Existing data describing the dependence of the concentrations of the defects S As , Zn Ga , Si Ga , Sb Ga , and EL2 in GaAs grown by organometallic vapor phase epitaxy on the partial pressures of arsine ( p As ) and the dopant-containing gases in the input gas stream are analyzed using a simple model. It is found that (1) As 4 is the dominant species of As in the vapor in equilibrium with the solid at the growth interface, (2) the electron concentration governing the charge state of the defect being formed is proportional to p As 3/4 independent of the dopant concentration, (3) the Fermi level during the defect formation process lies above the ionization levels of deep donors but below that of shallow donors, and (4) the atomic structure of the mid-gap electron trap, EL2, is stoichiometrically equivalent to the arsenic antisite, As Ga .