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Author: search.filters.author.Wang, PY

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Now showing 1 - 10 of 19
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    Temperature-dependent transport properties of n(+) GaAs/low-temperature GaAs/n(+) GaAs structures grown by molecular beam epitaxy
    (1996-06-01)
    Chen, JF
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    Chen, NC
    ;
    Chiu, SY
    ;
    Wang, PY
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    Lee, WI
    The temperature-dependent I-V characteristics of n(+) GaAs low-temperature GaAs(AlGaAs) n(+) GaAs structures in which the low-temperature layers were grown at 250, 350, and 450 degrees C were analyzed. Band conduction with an activation energy of 0.72 eV dominates at T>250 K. Hopping conduction dominates at T<250 K, where the resistivity was found to be insensitive to temperature. From this analysis, it is shown that Fermi level is pinned to an acceptorlike deep level of about 10(17) cm(-3), which lies at 0.72 eV below the conduction band. Measured capacitance can be described in terms of a parallel-plate capacitance with separation being equal to the expected growth thickness. Majority traps (electrons) were observed by deep-level transient spectroscopy with an activation energy about 0.72 eV, confirming the result of the resistivity analysis. In addition, the I-V characteristics were fitted to the simulated curves based on a simplified space-charge limited theory and the result was found to be consistent with the resistivity analysis. (C) 1996 American Institute of Physics.
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    Role of 0.66 eV dominant trap in annealed low-temperature grown molecular beam epitaxial GaAs
    (1998-02-01)
    Chen, NC
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    Wang, PY
    ;
    Chen, JF
    ;
    電子物理學系
    ;
    Department of Electrophysics
    The sample considered herein is an annealed low-temperature (LT) molecular beam epitaxially grown GaAs of n-LT-i-p structure with the LT layer grown at 300 degrees C. Characteristics involving the dominant trap level located at about 0.66 eV below the conduction band are obtained by analyzing the data of the admittance spectroscopy, capacitance-voltage, current-voltage, and frequency-dependent conductance experiments. This trap pins the fermi level of the LT layer and makes the LT layer semi-insulating. In this structure, the level interacts with both the conduction band and the valence band with a hole emission time constant characterized by an activation energy of 0.77 eV and a cross section of 1.1 X 10(-13) cm(2). This level is also an effective generation-recombination center when the temperature exceeds 300 K. (C) 1998 American Institute of Physics. [S0021-8979(98)04303-5].
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    Low frequency negative capacitance behavior of molecular beam epitaxial GaAs n-low temperature-i-p structure with low temperature layer grown at a low temperature
    (1998-03-02)
    Chen, NC
    ;
    Wang, PY
    ;
    Chen, JF
    ;
    電子物理學系
    ;
    Department of Electrophysics
    The GaAs sample under study is a n-low temperature-i-p structure grown by molecular beam epitaxy with a low-temperature (LT) layer grown at 300 degrees C and annealed at 620 degrees C for 1 h. Admittance measurements on this sample reveal a negative capacitance at low frequency. This work analyzes the origin of the negative capacitance and its corresponding frequency-dependent conductance by combining two current components: charging-discharging current and the inertial conducting current. Analysis results indicate that the activation energies and time constants of both current components closely resemble each other and should correspond to the same trap. Based on the results presented herein, we can conclude that the negative capacitance at low frequency provides evidence of a generation-recombination center with an activation energy of 0.77 eV in the LT layer. (C) 1998 American Institute of Physics.
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    Effects of high-resistivity, low-temperature layer in transient capacitance measurements of GaAs n-i-p structures
    (1998-10-15)
    Chen, JF
    ;
    Wang, PY
    ;
    Chen, NC
    ;
    電子物理學系
    ;
    Department of Electrophysics
    Deep-level transient spectroscopy and transient capacitance measurements are performed on a molecular-beam-epitaxially grown GaAs n-i-p diode with a 2000-Angstrom-thick low-temperature OLT)-grown layer immersed in its intrinsic region. The transient capacitance measurements reveal that the time constant and activation energy are the same for both the emission and capture processes. An equivalent circuit based on capacitance-frequency spectra is derived and used to obtain the resistivity values of the LT layer that are in agreement with experimental results. It is concluded that the transient capacitance observed corresponds to the resistance-capacitance time constant due to the LT-layer. In addition, the value of the activation energy is explained based on the equivalent circuit.
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    Transition of carrier distribution from a strained to relaxed state in InGaAs/GaAs quantum well
    (1999-03-01)
    Wang, PY
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    Chen, JF
    ;
    Wang, JS
    ;
    Chen, NC
    ;
    Chen, YS
    This work investigates the transition of carrier distribution from the strained to the relaxed state in In0.2Ga0.8As/GaAs quantum well by measuring capacitance voltage and analyzing x-ray diffraction. According to those results, there is carrier confinement in the In0.2Ga0.8As quantum well with well thickness less than the critical thickness. Increasing the well thickness beyond the critical thickness leads to a significant carrier depletion around the quantum well. Double-crystal x-ray rocking curves reveal that when InGaAs well thickness increases beyond the critical thickness, the interference pattern disappears and relaxation begins to occur from near the bottom InGaAs/GaAs interface while the top interface still remains strained. Results obtained from the critical thickness determined from x-ray diffraction correspond to the transition of carrier distribution, illustrating that the capacitance-voltage measurement is a rather effective means of determining the critical thickness. (C) 1999 American Institute of Physics. [S0021-8979(99)01505-4].
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    Observation of abnormal capacitance-frequency behavior in In0.12Ga0.88As/GaAs p-i-n superlattice grown at low temperature
    (1999-08-23)
    Chen, JF
    ;
    Wang, JS
    ;
    Wang, PY
    ;
    Wong, HZ
    ;
    電子物理學系
    Capacitance-frequency measurement is used to study In0.12Ga0.88As/GaAs p-i-n superlattice, with superlattice layer grown at 300 degrees C by molecular-beam epitaxy. Three traps are observed, and their parameters are consistent with those obtained from deep-level transient spectroscopy. Among these three traps, the trap (E-a = 0.45 +/- 0.02 eV, sigma = 6 +/- 4x10(-17) cm(2)) shows an abnormal increase of capacitance with increasing frequency, similar to that observed from the 0.66 eV trap in low-temperature grown GaAs p-i-n structure, suggesting that it is created by the low-temperature growth and is a generation-recombination center. This result also shows that the capacitance-frequency measurement is effective in studying the generation-recombination centers. (C) 1999 American Institute of Physics. [S0003-6951(99)01434-5].
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    Observation of carrier depletion and emission effects on capacitance dispersion in relaxed In0.2Ga0.8As/GaAs quantum wells
    (1999-10-18)
    Chen, JF
    ;
    Wang, PY
    ;
    Tsai, CY
    ;
    Wang, JS
    ;
    Chen, NC
    Strong changes in capacitance over frequency are found for highly relaxed In0.2Ga0.8As/GaAs quantum well. The high-frequency dispersion is explained by a resistance-capacitance time constant effect due to the existence of a high resistive layer while the low-frequency dispersion is due to carrier emission from traps. The high-resistance layer is created by carrier depletion when InGaAs thickness increases beyond the critical thickness. Excellent agreement is found between the data from capacitance-frequency spectra and deep-level transient spectroscopy, permitting us to conclude that both the carrier depletion and emission effects observed in capacitance-frequency spectra are due to the existence of an acceptor trap at 0.33 eV. This trap is generated when the InGaAs thickness is beyond its critical thickness and is due to defect states associated with misfit dislocations. (C) 1999 American Institute of Physics. [S0003-6951(99)02342-6].
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    Observation of a dominant EL2-like mid-gap trap in In0.12Ga0.88As/GaAs superlattice grown at low temperature by molecular beam epitaxy
    (1999-11-01)
    Chen, JF
    ;
    Wang, PY
    ;
    Wang, JS
    ;
    Wong, HZ
    ;
    電子物理學系
    Admittance spectroscopy is used to study a low-temperature (LT)-grown relaxed In0.12Ga0.88As/GaAs p-i-n superlattice. The capacitance-frequency spectra show two step-like trapping effects which are explained by the existence of two traps (E-a = 0.73 eV, sigma = 4.6 x 10(-11) cm(2) and E-a = 0.75 eV, sigma = 3.7 x 10(-15) cm(2)) in the LT-grown superlattice region. These two traps are the dominating defects observed in deep-level transient spectroscopy with one being a majority trap and the other being a minority trap. The emission parameters and photo-capacitance quenching effect for the 0.75 eV trap agree with those known for EL2 defects, suggesting that the EL2 defect is strongly enhanced in InGaAs/GaAs by LT growth.
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    Capacitance dispersion in n-LT-i-p GaAs structures with the low-temperature layers grown at different temperatures
    (1999-12-01)
    Chen, JF
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    Chen, NC
    ;
    Wang, PY
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    Wang, JS
    ;
    Weng, CM
    The electrical properties of annealed low-temperature GaAs are studied by investigating the frequency-dependent capacitance of n-LT-i-p structures with the low-temperature (LT) layers grown at different temperatures. Relative to the sample grown at 610 degrees C, the samples grown at 200, 300 and 400 degrees C show significant capacitance dispersions over frequency which is explained by the emission of carriers from traps. Based on a proposed band diagram where a dominating trap at 0.66-0.74 eV exists in the LT layers, the high-frequency dispersion is shown to be affected by resistance-capacitance (RC) time constant effects. From the mid-frequency capacitance versus voltage characteristics, the concentrations of the occupied traps are estimated to be approximate to 10(17) cm(-3) for samples grown at 200, 300 and 400 degrees C, which are found to be consistent with those obtained from analyzing the current-voltage characteristics of n(+)-LT-n(+) structures.
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    Admittance spectroscopy and thermal stimulation current for band-offset characteristics in AlAs/GaAs n(+)-p structures
    (2000-01-01)
    Chen, JF
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    Wang, JS
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    Wang, PY
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    Chen, NC
    ;
    Hsu, NC
    Admittance spectroscopy is used to study a molecular-beam epitaxially grown GaAs n(+)-p diode with 100-Angstrom-thick AlAs immersed in the lightly doped p-region. The measurements clearly show two trapping effects. Upon comparison with the reference sample without the AlAs layer, an equivalent circuit for the studied sample is developed. Based on this circuit, the admittance spectra are calculated and found to be consistent with the experimental spectra. From this result, the trap at E-a = 0.52 eV with a capture cross section 1.6 x 10(-14) cm(2) is believed to result from the resistance-capacitance time constant effect due to the thermionic emission of holes over the AlAs barrier and the activation energy corresponds to the AlAs/GaAs valence-band offset. The results of the thermal stimulation current further support this conclusion.