Browsing by Author "Hsiao, RS"

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1.3 mu m quantum dot vertical-cavity surface-emitting laser with external light injection
(2005-10-27)
Peng, PC
;
Chang, YH
;
Kuo, HC
;
Tsai, WK
;
Lin, G
A 1.3 mu m quantum dot vertical-cavity surface-emitting laser (QD VCSEL) with external light injection is presented, having been experimentally demonstrated. The QD VCSEL is fabricated on GaAs substrate. The 3 dB frequency response of the QD VCSEL based on the TO-Can package is enhanced from the free-running 1.75 to 7.44 GHz with the light injection technique.
1.3-mu m InAs-InGaAs quantum-dot vertical-cavity surface-emitting laser with fully doped DBRs grown by MBE
(2006-01-01)
Yu, HC
;
Wang, JS
;
Su, YK
;
Chang, SJ
;
Lai, FI
We report InAs-InGaAs quantum-dot vertical-cavity surface-emitting lasers (VCSELs) grown by molecular beam epitaxy with fully doped n- and p-doped AlGaAs distributed Bragg reflectors and including an AlAs layer to form a current and waveguiding aperture. The metal contacts are deposited on a topmost p(+) (GaAs)-Ga-. contact layer and on the bottom surface of the n(+)-GaAs substrate. This conventional selectively oxidized top-emitting device configuration avoids the added complexity of fabricating intracavity or coplanar ohmic contacts. The VCSELs operate continuous-wave at room temperature with peak output powers of 0.33 mW and differential slope efficiencies up to 0.23 W/A. The peak lasing wavelengths are near 1.275 mu m, with a sidemode suppression ratio of 28 dB.
Characterization of electron emission from relaxed InAs quantum dots capped with InGaAs
(2005-07-01)
Chen, JF
;
Hsiao, RS
;
Wang, CK
;
Wang, JS
;
Chi, JY
The effect of strain relaxation in a relaxed InAs quantum dot (QD) capped with InGaAs is investigated by admittance and deep-level transient spectroscopy (DLTS). Strain relaxation markedly increases the emission time in the QD region and extends carrier depletion to the bottom GaAs layer. The experimental data show the presence of relaxation traps in the QD region and the neighboring bottom GaAs.layer. The electron emission from the QD region is governed by a trap located at 0.17-0.21 eV below the QD ground state. The electron-escape process is identified as thermal activation at high temperatures and direct tunneling at low temperatures from the trap. In the bottom GaAs layer near the QD, DLTS reveals a relaxation trap at 0.37-0.41 eV relative to the GaAs conduction band. The energy difference between these two traps is comparable to the QD ground-state energy relative to the GaAs conduction-band edge, suggesting that the two traps may be the same trap which is pinned to the GaAs conduction band. The considerable difference between their properties may result from different atoms surrounding the trap. (c) 2005 American Institute of Physics.
Characterization of self-assembled InAs quantum dots with InAlAs/InGaAs strain-reduced layers by photoluminescence spectroscopy
(2005-04-15)
Chang, KP
;
Yang, SL
;
Chuu, DS
;
Hsiao, RS
;
Chen, JF
The optoelectronic characteristics of self-assembled InAs quantum dots (QDs) with strain-reduced layers (SRLs) were investigated using photoluminescence (PL) spectroscopy. Various SRLs that combine In0.14Al0.86As and In0.14Ga0.86As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs. (C) 2005 American Institute of Physics.
Continuous-wave high-power (320 mW) single mode operation of electronic vertically coupled InAs/GaAs quantum dot narrow-ridge-waveguide lasers
(2005-12-01)
Wang, JS
;
Lin, G
;
Hsiao, RS
;
Yang, CS
;
Lai, CM
High-power 3 mu m-wide narrow-ridge-waveguide lasers with ten stacks of electronic vertically coupled InAs/GaAs quantum dots in the active region were demonstrated. Unlike that from conventional uncoupled InAs quantum dot lasers, a narrow lasing spectrum was observed because the carriers tunneled in the vertical direction. Continuous-wave operation in single lateral mode yielded a kink-free output power of 320 mW with an efficiency of 0.46 W/A , and a sensitivity of lasing wavelength to temperature of 0.28 nm/K.
Effect of growth rate on the composition fluctuation of InGaAsN/GaAs single quantum wells
(2006-06-15)
Chen, JF
;
Hsiao, RS
;
Hsieh, PC
;
Wang, JS
;
Chi, JY
Effect of growth rate on the composition fluctuation is investigated in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells (QWs) by photoluminescence (PL), transmission electron microscopy, and admittance spectroscopy. In an InGaAsN layer grown at a normal growth rate, the PL spectra show a low-energy bump at the tail of an InGaAsN emission, suggesting the presence of composition fluctuation. Lowering the growth rate degrades the composition fluctuation by segregating into bimodal phases of an InGaAsN and InGaAs-rich phase. Further lowering the growth rate leads to a three-dimensional growth and enhances the InGaAs-rich phase. The carrier distribution for the InGaAsN layer grown at the normal rate shows a carrier bump at the tail of a strong accumulation peak, suggesting the presence of an electron state below the QW ground state. The admittance spectroscopy shows that the activation energy (32 meV) of this electron state is comparable to the energy separation (30 meV) between the InGaAsN emission and the low-energy bump, and thus it is possible that the composition fluctuation actually induces an electron state closely below the QW ground state. (c) 2006 American Institute of Physics.
Effect of incorporating an InAlAs layer on electron emission in self-assembled InAs quantum dots
(2006-01-01)
Chen, JF
;
Hsiao, RS
;
Hsieh, MF
;
Wang, JS
;
Chi, JY
We perform capacitance-voltage and admittance spectroscopy to investigate the effect of incorporating an InAlAs layer before an InGaAs cap layer on electron emission in self-assembled InAs quantum dots (QDs). We show that this incorporation of a high potential barrier increases the emission time of the electrons thermally activated from the QD ground to the first excited state. The energy separation between the ground and first excited states in the conduction band increases from 57.2 to 79.1, to 89.2, and to 95.6 meV with increasing the thickness of the InAlAs layer from 0 to 10, to 14, and to 20 A. Combining with photoluminescence (PL) data, the ratios of the energy separation between the ground and first excited states in the conduction band and valence band are determined to be 7.3:2.7 and 7.8:2.2 for 0 and 10 A InAlAs, respectively. In addition, this incorporation is shown to blueshift the PL first excited state much larger than the ground state.
Effect of nitrogen incorporation into InAs layer in InAs/InGaAs self-assembled quantum dots
(2005-09-01)
Chen, JF
;
Hsiao, RS
;
Chen, YC
;
Chen, YP
;
Hsieh, MT
We present the results of nitrogen. incorporation into the InAs layer in InAs/InGaAs quantum dots (QDs). We show that this incorporation causes an asymmetric photoluminescence (PL) line shape and abnormally, large redshift of the PL peak from the quantum dots as temperature increases. In addition, this incorporation causes a large series resistance and a rapid increase in reverse current at a bias corresponding to the QD region. This effect is due to the formation of a deep trap at 0.34-0.41 eV, which depletes the carriers in the QD region. This depletion gives rise to a geometric resistance-capacitance time-constant effect for the ac conductivity of the free electrons in the top GaAs layer. This trap markedly alters the emission properties of the QD structure. The ac conductivity of the QD structure is governed by the thermal activation of trapped electrons rather than the electron emission from the QD confined states. This incorporation significantly increases the electron emission time from the QD region and, thus, can be used intentionally to modify the emission properties of the QD structure.
Evolution of conduction and interface states of laterally wet-oxidized AlGaAs with oxidation time
(2006-01-15)
Chen, JF
;
Hsiao, RS
;
Hung, WK
;
Wang, JS
;
Chi, JY
The conduction and interface states of laterally wet-oxidized GaAs-AlGaAs-GaAs structures after various oxidation times are investigated. Effective current blocking is achieved after 150 min oxidation and the conduction of current through the oxidized AlGaAs layer is controlled by the Poole-Frenkel mechanism, from which a relative dielectric constant of 7.07 is obtained. At an oxidation time of 15 min, capacitance-voltage spectra exhibit capacitance dispersion over frequency, implying the presence of an interface state. The intensity of the dispersion increases with increasing the oxidation time and admittance spectroscopy reveals a significant interface state at similar to 0.28 eV at 45 min. Further increasing the oxidation time to 150 min broadens the interface state to a set of continuous interface states from 0.19-0.31 eV with decreasing densities from 3x10(11) to 0.9x10(11) eV(-1) cm(-2) and generates fixed charges of about 9.1x10(11) cm(-2) in the oxidized layer. By comparison to a similar trap in a relaxed InGaAs/GaAs, the interface state is tentatively assigned to the interaction of residual As with dislocations. (c) 2006 American Institute of Physics.
High nitrogen content InGaAsN/GaAs single quantum well for 1.55 mu m applications grown by molecular beam epitaxy
(2004-02-15)
Wang, JS
;
Kovsh, AR
;
Hsiao, RS
;
Chen, LP
;
Chen, JF
The growth of high nitrogen content InGaAsN/GaAs single quantum well (SQW) for 1.55 mum applications on GaAs substrates using solid source molecular beam epitaxy and radio frequency plasma nitrogen source is reported. The nitrogen composition was determined using an X-ray diffractometer combined with dynamic simulation. The crystal and optical qualities of highly strained InGaAs/GaAs SQW grown at low temperature can be significantly improved by nitrogen incorporation due to reducing the lattice mismatch. Without the formation of additional nonradiative recombination in InGaAsN SQW with nitrogen composition up to 4.1% which corresponds to wavelength of 1.46 mum was achieved. The longest room-temperature PL peak wavelength obtained in this study is 1.59 mum by increasing the nitrogen composition up to 5.3%. And, the photoluminescence intensity of high nitrogen content InGaAsN SQW can be improved significantly by decreasing the growth temperature due to suppression of the phase separation of InGaAsN alloy. Our results show the potential for the fabrication of 1.55 mum InGaAsN QW lasers on GaAs substrates. (C) 2003 Elsevier B.V. All rights reserved.
High-performance 30-period quantum-dot infrared photodetector
(2005-05-01)
Chou, ST
;
Lin, SY
;
Hsiao, RS
;
Chi, JY
;
Wang, JS
In this article, quantum-dot infrared photodetectors (QDIPs) with 10- and 30-period InAs/GaAs quantum-dot structures are investigated. High responsivity of 2.37 A/W and detectivity of 2.48 X 10(10) cm Hz(1/2)/W for 30-period QDIPs under 10 K are observed at -2.7 and 1.2 V, respectively. Almost symmetric photocurrents and dark currents under positive and negative biases are observed for both devices, which indicate a minor influence of the wetting layer on the performance of QDIPs. Lower dark current and increased photocurrent for the 30-period QDIPs would predict a better performance for devices with over a 30-period QD structure. (c) 2005 American Vacuum Society.
Molecular-beam-epitaxy growth of high-quality InGaAsN/GaAs quantum well lasers emitting at 1.3 mu m
(2004-11-01)
Wang, JS
;
Hsiao, RS
;
Lin, G
;
Lin, KF
;
Liu, HY
Molecular-beam-epitaxy growth of high structural and optical-quality InGaAsN/GaAs quantum wells (QW) has been investigated. The material quality can be improved significantly by using low-temperature growth to suppress the phase separation. High-performance ridge-waveguide InGaAsN/GaAs single QW lasers emitting at 1.3 mum have been demonstrated. Infinite-cavity-length threshold-current density of 400 A /cm(2), internal quantum efficiency of 96%. and a slope efficiency of 0.67 W/A for a cavity length L=1 mm were obtained. A TO46 packaging laser shows sin-le lateral-mode kink-free output power of more than 200 mW with a maximum total wallplug efficiency of 29% at room temperature under continuous wave (cw) operation. Moreover. 1.3 Am InGaAsN/GaAs QW vertical-cavity surface-emitting lasers with a threshold current density lower than 2 KA/cm(2) at room temperature have been achieved. We obtained multimode cw output power and slope efficiency in excess of 1 mW and 0.15 W/A. respectively. (C) 2004 American Vacuum Society.
N incorporation into InGaAs cap layer in InAs self-assembled quantum dots
(2005-12-01)
Chen, JF
;
Hsiao, RS
;
Hsieh, PC
;
Chen, YJ
;
Chen, YP
This study presents the results of incorporating N into self-assembled InAs quantum dots (QDs) capped with an InGaAs cap layer. Experimental results indicate that such incorporation can redshift the QD ground state and decrease the energy spacing between the QD ground and first excited states. However, this incorporation reduces the potential barrier of the cap layer, increasing the electron escape from the QDs. Capacitance-voltage profiling shows that a broad shoulder corresponding to the electron emission from the QD ground to first-excited state cannot be resolved from the peak related to the electron emission from the excited states upon this incorporation. This finding implies that this incorporation reduces the energy spacing between the QD ground and first-excited states in the conduction band, thus correlating well with the photoluminescence data. In contrast, incorporating N directly into the InAs QD produces no redshift of the emission wavelength but introduces a deep trap at similar to 0.21 eV that depletes the electrons in the QDs. (c) 2005 American Institute of Physics.
Properties of defect traps in triple-stack InAs/GaAs quantum dots and effect of annealing
(2004-09-15)
Chen, JF
;
Hsiao, RS
;
Shih, SH
;
Wang, PY
;
Wang, JS
The electrical and optical properties of the defect traps, with and without annealing, in InAs/GaAs quantum dots (QDs) emitting at 1.3 mum are investigated by capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and photoluminescence (PL). When increasing the InAs thickness to 3 ML, an abnormal temperature dependence of the C-V characteristic was observed in the triple-stack InAs/GaAs QD sample. This temperature dependence is attributed to the defect levels at 0.39 and 0.54 eV observed in DLTS. The level at 0.39 eV, found in the top GaAs barrier, is probably related to the relaxation-induced dislocations. The level at 0.54 eV is found close to the QD region. Rapid thermal annealing can reduce the concentrations of both levels. Comparing with PL result, which shows a blueshift of 140 meV and linewidth narrowing in the QD emission by annealing at 800degreesC, the level at 0.54 eV is speculated to be strain- or relaxation-related defects in the interface between the QDs and the barrier. Removal of this level by high-temperature RTA is important since this level lies close to the QDs and influences the optical quality of the QDs.
Single mode 1.3 mu m InGaAsN/GaAs quantum well vertical cavity surface emitting lasers grown by molecular beam epitaxy
(2004-12-01)
Hsiao, RS
;
Wang, JS
;
Lin, KF
;
Wei, L
;
Liu, HY
The growth by molecular-beam-epitaxy of high-quality 1.3 mum InGaAsN/GaAs quantum wells (QW) intra-cavity contacted vertical cavity surface emitting lasers (VCSELs) was demonstrated. Low-temperature growth, which suppresses the phase separation significantly improves material quality in the active region. Room-temperature continuous wave (RT-CW) single mode output power of 0.75 mW with an initial slope efficiency of 0.17 W/A and a side mode suppression ratio of 40 dB at a lasing wavelength of as long as 1304 nm were obtained.
Single-mode monolithic quantum-dot VCSEL in 1.3 mu m with sidemode suppression ratio over 30 dB
(2006-03-01)
Chang, YH
;
Peng, PC
;
Tsai, WK
;
Lin, G
;
Lai, F
We present monolithic quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs) operating in the 1.3-mu m optical communication wavelength. The QD VCSELs have adapted fully doped structure on GaAs substrate. The output power is similar to 330 mu W with slope efficiency of 0.18 W/A at room temperature. Single-mode operation was obtained with a sidemode suppression ratio of > 30 dB. The modulation bandwidth and eye diagram in 2.5 Gb/s was also presented.
Singlemode InAs quantum dot photonic crystal VCSELs
(2005-09-29)
Yang, HPD
;
Chang, YH
;
Lai, FI
;
Yu, HC
;
Hsu, YJ
An InAs quantum dot photonic crystal vertical-cavity surface-emitting laser (QD PhC-VCSEL) for fibre-optic applications is first demonstrated. Single fundamental mode CW output power of 0.2 mW has been achieved in the 1300 nm range, with a threshold current of 4.75 mA. Side-mode suppression ratio larger than 40 dB has been observed over the entire thermally limited operation range.
Strain relaxation in InAs/InGaAs quantum dots investigated by photoluminescence and capacitance-voltage profiling
(2005-10-03)
Chen, JF
;
Hsiao, RS
;
Chen, YP
;
Wang, JS
;
Chi, JY
We present detailed studies of the onset of strain relaxation in InAs/InGaAs quantum dots. We show that the ground-state photoluminescence (PL) emission redshifts with increasing the InAs coverage before relaxation and blueshifts when relaxation occurs. PL spectra of the relaxed samples show two predominant families of dots with very different temperature-dependent efficiency. By comparison we show that the dots emitting at long wavelength are degraded by relaxation while the dots emitting at short wavelength remain coherently strained. Consequently, the PL spectra are dominated by the dots emitting at short wavelength, leading to the observed blueshift. This result suggests that the relaxation does not occur uniformly. In addition, we show that the relaxation occurs in the dot bottom interface. (C) 2005 American Institute of Physics.
Temperature-dependent optical properties of In0.34Ga0.66As1-xNx/GaAs single quantum well with high nitrogen content for 1.55 mu m application grown by molecular beam epitaxy
(2006-05-15)
Lai, FI
;
Kuo, SY
;
Wang, JS
;
Hsiao, RS
;
Kuo, HC
The temperature dependence of optical properties of InGaAsN/GaAs single-quantum wells grown by solid source molecular beam epitaxy (MBE) with N contents varied from 0% to 5.3% was investigated by photoluminescence (PL). The evolution of the peak positions of InGaAs/GaAs sample are in agreement with the empirical Varshni model. However, pronounced temperature-dependent S-shaped peak positions and N-shaped linewidth were observed in PL spectra while increasing nitrogen concentration. The activation energy of InGaAsN/GaAs single quantum well (SQWs) is observed to decrease with nitrogen incorporation, which is contrary to the expectation of the bandgap reduction. This phenomenon suggests that the existence of defect-related nonradiative processes is due to nitrogen incorporation. The results of measurement demonstrate that the nitrogen incorporation into the InGaAsN has strong influence not only on carrier localization but also on the optical quality. In addition, the growth of high nitrogen content (5.3%) shows that the InGaAsN might be the potential candidate for long-wavelength optoelectronic devices. (c) 2006 Elsevier B.V. All rights reserved.
Thickness dependence of current conduction and carrier distribution of GaAsN grown on GaAs
(2005-10-01)
Chen, JF
;
Hsiao, RS
;
Hsieh, MT
;
Huang, WD
;
Guo, PS
Thickness dependence of the properties of GaAsN grown on GaAs was investigated by characterizing GaAs/GaAS(0.982)N(0.018)/ GaAs Schottky diodes by current-voltage (I-V), capacitance-voltage (C-V) profiling and deep-level transient spectroscopy (DLTS). I-V characteristics show a considerable increase in the saturation current when the GaAsN thickness is increased from 60 to 250 A. As GaAsN thickness is increased further, the I-V characteristic deviates from that of a normal Schottky diode with a large series resistance. These I-V characteristics correlate well with carrier distribution. In thick GaAsN samples, C-V profiling shows carrier depletion in the top GaAs layer and frequency-dispersion accumulation in the GaAsN layer. DLTS spectra show that the carrier depletion in the top GaAs layer is due to an EL2 trap and the frequency-dispersion accumulation is due to the removal of electrons from a trap at 0.35 eV in the GaAsN layer. Increasing the GaAsN thickness markedly increases the magnitude of both traps. The large series resistance in thick GaAsN samples is due to EL2 that markedly depletes the top GaAs layer.