J. W. Huang

Electrical characterization of Mg‐doped GaN grown by metalorganic vapor phase epitaxy

We have applied frequency‐dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot‐and‐ring Schottky diodes using Au/Ti were fabricated. Frequency‐dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high‐frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity‐related acceptor level in the higher Mg‐doped sample with an activation energy of 136 meV. For the lower Mg‐doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which a...

Alkoxide precursors for controlled oxygen incorporation during metalorganic vapor phase epitaxy GaAs and Al x Ga 1−x As growth

Controlled oxygen incorporation in GaAs using Al-0 bonding based precursors, dimethyl aluminum methoxide (DMALO) and diethyl aluminum ethoxide (DEALO), is presented in this investigation. A comparison study of oxygen incorporation kinetics between nominally undoped AlxGa1−xAs using trimethyl aluminum and DMALO-doped GaAs suggests that DMALO is one of the most important oxygen-bearing agents responsible for unintentional oxygen incorporation in AlxGa1−xAs. Controlled oxygen doping using DEALO is reported for the first time. Oxygen incorporation behavior, especially on the effect of the V/III ratio, was found to be quite different from the case of DMALO, mainly due to the differences between methyl- and ethyl-based growth chemistries. Physical, electrical, and optical properties of these oxygen-doped GaAs are also reported.

Multiple deep levels in metalorganic vapor phase epitaxy GaAs grown by controlled oxygen incorporation

Oxygen intentionally introduced into GaAs, grown through the metalorganic vapor phase epitaxy process, is shown to introduce a controlled series of deep levels. A novel, commercially available, oxygen precursor, (C2H5)2AlOC2H5, was used as the oxygen source. Capacitance measurements have revealed compensation of both donors and acceptors in these materials when using this source. The determination of the deep level structure of these films has been carried out through the use of deep level transient spectroscopy (DLTS). The DLTS investigation, carried out on GaAs p+‐n homojunctions, indicates that unlike the case of bulk oxygen‐doped GaAs (GaAs:O), several deep levels are introduced and directly associated with the intentional oxygen introduction. Two principal traps are found to be located at 0.95 and 0.75 eV below the conduction‐band edge, with several other minor traps being observed. These intentionally introduced deep levels have been used to form highly resistive GaAs, providing an analog to the cur...

Chemical and physical effects in oxygen incorporation during the metalorganic vapor phase epitaxial growth of GaAs

Combined growth, electrical and morphological studies of the influence of oxygen incorporation were carried out on metalorganic vapor phase epitaxy (MOVPE) grown GaAs. The impact of oxygen incorporation on the growth front morphology has been systematically investigated. Oxygen is incorporated into the growing film through the use of an Al-based precursor, (C 2 H 5 ) 2 AlOC 2 H 5 , which contains Al directly bonded to an oxygen atom. The oxygen appears to be preferentially incorporated at the metal-terminated steps. The presence of one or more Al atoms at the step edge is believed to be responsible for the incorporation of electrically active oxygen into the lattice. Oxygen at the growth front, particularly at the step edges, leads to the gradual roughening of the surface structure. High levels of oxygen, [O] ≥ 10 18 cm -13 , lead to the breakdown of the periodic surface structure found in nominally undoped MOVPE GaAs with a very rough hillock structure resulting. Models for the impact of oxygen on the growth front evolution are presented. The study of the simpler GaAs :O system can provide a basis for understanding the role of oxygen in more complex semiconductor systems.

The effects of temperature and oxygen concentration on the photoluminescence of epitaxial metalorganic vapor‐phase epitaxy GaAs:O

Semi‐insulating epitaxial GaAs:O prepared in a metalorganic vapor‐phase epitaxy growth process using DEALO [(C2H5)2AlOC2H5] as the oxygen source has been characterized by temperature‐dependent (12–300 K) photoluminescence. Oxygen‐related deep level photoluminescence bands were detected at ∼0.8 and ∼1.1 eV. The relative intensities of the two bands were sensitive to both oxygen concentration and temperature. At a given temperature, an increase in oxygen concentration led to an increase in the intensity of the lower energy band relative to the higher energy band. A similar effect occurred at a given oxygen concentration as the temperature was raised. Band edge luminescence was also measured and was observed to quench when the oxygen concentration exceeded ∼1018 cm−3. The results indicate that oxygen is incorporated differently in epitaxial GaAs than in bulk GaAs. We propose that the difference is due to the incorporation of Al when DEALO is used in the growth of epitaxial GaAs:O. We suggest equally plausibl...

Ultrafast carrier trapping in oxygen-doped metal-organic vapor phase epitaxy GaAs

We have experimentally investigated the ultrafast carrier dynamics in GaAs grown by metal-organic vapor phase epitaxy with an oxygen precursor. Using a time-resolved reflection ellipsometric technique, we measured the carrier-induced refractive and absorptive index changes as a function of oxygen and aluminum doping concentrations. The free carrier trapping time is inversely proportional to the aluminum-oxygen based complex concentration and can be as short as 300 fs. The material is also highly resistive and promises to be an excellent candidate for optoelectronic applications requiring short carrier lifetime and high dark isolation.

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy InxGa1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in InxGa1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of InxGa1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In0.53Ga0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.

Compensation of shallow impurities in oxygen‐doped metalorganic vapor phase epitaxy grown GaAs

Intentional oxygen incorporation, using diethyl aluminum ethoxide [(C2H5)2AlOC2H5] during metalorganic vapor phase epitaxy GaAs was found to compensate C and Zn shallow acceptors as well as Si and Se shallow donors, due to the oxygen‐related multiple deep levels within the GaAs band gap. Deep level transient spectroscopy (DLTS) was used to characterize the energy levels associated with these oxygen deep centers. The total measured trap concentration from DLTS can account for the observed compensation in n‐type GaAs:O. The total trap concentration in p‐type GaAs:O, however, was found to be lower than the observed compensation by a factor of ∼100. These oxygen deep centers exhibit multiple electronic states which have been associated with the local number of Al nearest neighbors and the microscopic structure of the defect. The concentration and nature of these deep levels were not influenced by the chemical identity of the shallow dopants.

Influence of oxygen on surface morphology of metalorganic vapor phase epitaxy grown GaAs (001)

Atomic force microscopy has been used to investigate the influence of controlled oxygen incorporation on the surface morphology of GaAs films grown by metalorganic vapor phase epitaxy (MOVPE). Oxygen influences the periodic morphology observed in GaAs surfaces, with concentrations about 1018 cm−3 leading to a breakup of the periodicity. To account for these observations, we propose a model in which oxygen preferentially attaches at steps with a subsequent reduction in step mobility and a concomitant increase in the surface roughness.

Oxygen‐based deep levels in metalorganic vapor phase epitaxy indium gallium arsenide

We have studied the defect engineering in metalorganic vapor phase epitaxy InxGa1−x As by controlled oxygen doping. Diethylaluminum ethoxide (DEALO) was used as an oxygen precursor to provide the intentional deep level incorporation. DEALO doping in InxGa1−xAs:Si with x≤0.25 resulted in the reduction in carrier concentrations. The Al and O incorporation with a DEALO mole fraction was weakly dependent on alloy composition for x≤0.25. The degree of electrical compensation, however, decreased as the In content increased at the same oxygen content. Deep level transient spectroscopy investigations on a series of InxGa1−xAs:Si:O samples with x ranging from 0 to 0.18 reveal a set of oxygen‐derived deep levels, similar to those found in DEALO‐doped GaAs. These characteristic deep levels appear to remain at a relatively constant energy with respect to the valence band, as compared to the rapid decrease in the conduction band of InxGa1−xAs with x.