DX Centers In AlxGa1-xAs Research Articles

Localized-capture-state model for the capture kinetics of the DX center in AlxGa1-xAs.

An alternative model for the kinetics of electron capture at DX centers in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As is presented. The model assumes capture through a localized capture state resonant with the conduction band. Photoelectron decay transients in a sample of Si-doped ${\mathrm{Al}}_{0.28}$${\mathrm{Ga}}_{0.72}$As were measured as a function of both temperature and light exposure time. The decay rate depends on both the instantaneous electron concentration and the electron concentration at the start of the decay. This result gives direct evidence for the distribution of capture-state energy levels assumed in the model.

Comment on "Negative-U property of the DX center in AlxGa1-xAs:Si"

A contradiction between conclusions derived by M. F. Li et al. [Phys. Rev. B 40, 1430 (1989)] and J. E. Dmochowski and L. Dobaczewski [Semicond. Sci. Technol. 4, 579 (1989)] on the applicability of a simple single-level model of the DX center with negative-U properties to the Hall experimental data for n-type ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As is discussed. The suggestion of Li et al., that more than one type of impurity center is present in the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As alloy, is likely to be correct, but it is shown that they may all possess a negative-U DX-type level.

Double-Peak Emission Rate Spectrum of DX-Centers in AlxGa1-xAs

Emission rate spectra S(λ) of the DX-centers in AlxGa1-xAs were studied for dopants, such as Te, Sn, Si and Se, using the SADLTS (spectral analysis of deep level transient spectroscopy) method. The double peak emission rate spectra were observed for these DX-centers in AlxGa1-xAs at around x=0.5 of Al mole fraction. The band effect (crossover of L-band and \\varGamma-band) is the dominant contribution to the rather broadened spectra of DX-centers appearing in the conventional DLTS.

The DX Center: Evidence for Charge Capture Via an Excited Intermediate State

AbstractWe review three important experimental results which suggest that electron capture and emission by the DX center in AlxGa1-xAs proceeds via an excited intermediate state: the very different dependencies of the thermal capture and emission rates on alloy composition, the exponential dependence of the thermal capture rate on the quasi-equilibrium Fermi energy, and the thermal activation of the hot electron capture rate. None of these results is readily explained by a conventional lattice relaxation model, in which an electron is captured directly from the lowest lying band edge, but each can be simply explained if the dominant channel for multiphonon capture is via a transition state which lies well above the band edge. This picture is consistent with recent pseudopotential calculations which predict that the lattice relaxed state (the DX state) is stabilized by capture of more than one electron, since such a model naturally admits the possibility of an intermediate one-electron state.

Spectral Analysis of Deep Level Transient Spectroscopy (SADLTS) of DX-centers in AlxGa1-xAs:Sn

Emission rate spectra S(λ, T) of DX-centers in AlxGa1-xAs:Sn for x=0.35, 0.45, 0.55, 0.65 and 0.75 were obtained from the transient capacitance waveform ΔC(t, T) by the spectral analysis proposed in our previous paper. S(λ, T)'s were distributed over the range λ∼10∼103 between 170∼200 K and showed double peak features for x=0.35, 0.45 and 0.55. S(λ, T)'s broaden, shift to higher λ and decrease their peak heights at higher temperatures. Assuming Gaussian distribution for both capture cross section σ and activation energy E, the width of the activation energy ΔE is estimated to be 10∼16 meV and largest at x=0.45, while the relative broadening in the capture cross section is found to be Δσ/σ0∼1/3 from the shape of S(λ, T). The possible origin of the double peaks is tentatively assigned to DX-to-X conduction band and DX-to-L conduction band excitation for x=0.45 and 0.55.

Deep Electron Traps in AlAs-GaAs Superlattices as Studied by Deep-Level Transient Spectroscopy

Deep electron traps in Si-doped AlAs-GaAs superlattices (SLs) grown by MBE have been investigated using deep-level transient spectroscopy (DLTS). The concentration of the characteristic electron trap (E2 trap) in the SLs increases upon decreasing the period of SL and increasing the Si doping concentration. The E2 trap concentration for uniformly Si-doped SLs is more than one order higher than that for SLs doped selectively at the middle part of each AlAs and GaAs layer. The E2 traps have properties similar to the so-called DX centers in AlxGa1-xAs, and they exist only in the AlAs-GaAs interfaces. The different activation energies of the traps in SLs and Al0.3Ga0.7As can be explained in terms of carrier emission from the E2 trap to the mini-band levels of the SLs and to the conduction band minimum of the alloys, respectively.