A detailed investigation of the D-X center and other trap levels in GaAs-Al x Ga 1-x As modulation-doped heterostructures grown by molecular-beam epitaxy
TL;DR: In this article, the authors re-examined the results and analysis of capacitance transient spectroscopy measurements made on modulation-doped heterostructures suitable for the fabrication of field effect transistors.
Abstract: We have re-examined the results and analysis of capacitance transient spectroscopy measurements made on modulation-doped heterostructures suitable for the fabrication of field-effect transistors. It is seen that conventional analysis of data can lead to erroneous results and a new model, which includes the contribution of the capacitance at the heterointerface, is presented. Most of the observed anomalous behavior related to trap emission can now be explained. Six main electron traps are present in single-layer Al x Ga 1-x As, grown by molecular-beam epitaxy, and in device-quality GaAs-Al x Ga 1-x modulation-doped heterostructures. These range in energy from 0.40 to 0.91 eV in thermal ionization energy. The well known D-X center in Si-doped Al x Ga l-x As layers is composed of two closely spaced levels, DX1 and DX2, with ionization energies of 0.48 and 0.52 eV, respectively. At very low Si,doping levels, only DX2 is dominant, but at doping levels > 1018cm-3, both DX1 and DX2 become comparable in concentration. The optical ionization properties of these levels were also measured and it is seen that the optical lineshapes differ markedly for the two centers. The peak photoionization cross sections occur at spectral energies of 1.25 and 1.38 eV for DX1 and DX2, respectively. The nature and symmetry of the centers have been studied by measurements on layers of different orientations.
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TL;DR: In this article, it was shown that the properties of the deep level when resonant with the conduction band are similar to its characteristics when it is the stable state of the donor.
Abstract: D X centers, deep levels associated with donors in III‐V semiconductors, have been extensively studied, not only because of their peculiar and interesting properties, but also because an understanding of the physics of these deep levels is necessary in order to determine the usefulness of III‐V semiconductors for heterojunction device structures. Much progress has been made in our understanding of the electrical and optical characteristics of D X centers as well as their effects on the behavior of various device structures through systematic studies in alloys of various composition and with applied hydrostatic pressure. It is now generally believed that the D X level is a state of the isolated substitutional donor atom. The variation of the transport properties and capture and emission kinetics of the D X level with the conduction‐band structure is now well understood. It has been found that the properties of the deep level when it is resonant with the conduction band, and is thus a metastable state, are similar to its characteristics when it is the stable state of the donor. And it has been consistently found that there is a large energy difference between the optical and thermal ionization energies, implying that this deep state is strongly coupled to the crystal lattice. The shifts in the emission kinetics due to the variation in the local environment of the donor atom suggest that the lattice relaxation involves the motion of an atom (the donor or a neighboring atom) from the group‐III lattice site toward the interstitial site. Total energy calculations show that such a configuration is stable provided that the donor traps two electrons, i.e., has negative U. Verification of the charge state of the occupied D X level is needed as well as direct evidence for its microscopic structure.
673 citations
TL;DR: In this article, a large-signal digital-switching transistor characterization methodology is developed to estimate the parameters of a high-electron-mobility transistor and to obtain the large signal characteristics of this device on a picosecond time scale.
Abstract: Recent advances in state-of-the-art optoelectronic techniques applied to areas pertinent to transistor small-signal and large-signal characterization are discussed. The aspects of optoelectronic techniques for electrical signal measurement, generation, and transmission are studied. On the basis of these results, a large-signal digital-switching transistor characterization methodology is developed. This methodology is used to estimate the parameters of a high-electron-mobility transistor and to obtain the large-signal characteristics of this device on a picosecond time scale. The measurements are compared to a SPICE-based time-domain model. The time-domain measurement technique is extended to obtain two-port frequency-domain characteristics of another, similar transistor with a 100-GHz bandwidth. These results compare favorably to conventional HP8510 network analyzer measurements over a common frequency span of 40 GHz. >
80 citations
TL;DR: A photoluminescence emission band at 830 nm has been detected in single heterojunction quantum well structures (modulation-doped structures) in the range of 250-400 K.
Abstract: A photoluminescence emission band at 830 nm has been detected in single heterojunction quantum well structures (modulation‐doped structures) in the range of 250–400 K. This emission band is observed neither in heterojunction structures without a two‐dimensional electron gas (2DEG), nor in n+ AlGaAs and GaAs. The intensity of the emission band increases as the mobility of the samples with 2DEG and shows excitonic behavior in its variation with incident laser excitation intensity. This photoluminescence emission was observed in samples grown by both molecular beam epitaxy and by organometallic vapor phase epitaxy. This effect may be useful as a rough identification of high quality, modulation‐doped heterostructures.
39 citations
TL;DR: In this paper, a fine structure of the DX center thermal emission spectra under adequate filling pulse and sampling window times is revealed, which indicates that the origin of the fine structure and the nonexponential behavior of the thermal emission processes is the discrete broadening of σ∞n due to the alloy effect.
Abstract: Deep level transient spectroscopy in Si‐ and Sn‐doped GaAlAs reveals a fine structure of the DX center thermal emission spectra under adequate filling pulse and sampling window times. This structure is reproducible in samples with Al mode fractions near 30% but it is not detectable in samples with 85% Al content. All resolved peaks of this fine structure have the same thermal emission energy but quite different capture cross section (σ∞n). This fact indicates that the origin of the fine structure and of the nonexponential behavior of the thermal emission processes is the discrete broadening of σ∞n due to the alloy effect.
35 citations
TL;DR: In this article, an Arrhenius-type expression for the emission rate of electrons from a quantum well was derived on the basis of detailed balance principles and applied to a 150-A In0.2Ga 0.8As/Al 0.16Ga0.84As strained single quantum well grown by molecular beam epitaxy.
Abstract: An Arrhenius‐type of expression is derived for the emission rate of electrons from a quantum well on the basis of detailed balance principles. The formulation is applied to a 150‐A In0.2Ga0.8As/Al0.16Ga0.84As strained single quantum well grown by molecular beam epitaxy. From an analysis of the data it is possible to estimate the conduction band offset ΔEc, which may be extremely useful for strained systems.
30 citations