-
[show abstract]
[hide abstract]
ABSTRACT: We report voltage-tunable 3-5 μm & 8-12 μm dual-band detection in the InAs/Al0.3Ga0.7As/In0.15Ga0.85As confinement-enhanced dots-in-a-well quantum dot infrared photodetectors. The capability in temperature sensing is also demonstrated. Distinct response peaks at 5.0 μm and 8.6 μm were observed in the photocurrent spectra with working temperature up to 140K. The two peaks correspond to the transition paths from the quantum dot ground state to the quantum well state and the quantum dot excited state, respectively. At 77K, the response ratio of the 8.6 μm peak over the 5.0 μm peak changes from 0.29 at -3V to 5.8 at + 4.8V. Excellent selectivity between the two peaks with bias voltage makes the device attractive for third-generation imaging systems with pixel-level multicolor functionality.
Optics Express 05/2012; 20(10):10484-9. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Vertically coupled InAs-GaAs quantum-dot infrared photodetectors (QDIPs) were studied in this letter. With vertically coupled quantum dots (QDs), the QDs in the same column share the same electronic states which remove the QD size variation effect in the growth direction and result in a narrow response band and higher peak quantum efficiency. The coupled states increase the capture probability and also facilitate the carrier flow among QD layers. The frequency response of vertically coupled QDIPs is much faster than that of the conventional ones.
IEEE Photonics Technology Letters 07/2010; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nonlinear HBT models are presented for 15 W power amplifiers with superior back-off linearity. Each amplifier consists of 8 Building Blocks of 28 V InGaP/GaAs HBT. The P1dB is 42 dBm. The models are based on the AHBT model for the Building Block (1 BB) reported previously. The model for the amplifier at 2.14 GHz is scaled from the AHBT model for 1 BB whereas the model for the amplifier at 940 MHz is a revised model due to modifications in the HBT layout designed for that frequency. Key device parameters are adjusted based on the changes in layout and the measured device characteristics to avoid a standard time consuming modeling process. Both models can precisely simulate all aspects of nonlinear performance of amplifiers such as output power, gain, P1dB, operation current, efficiency, IM3 and ACLR. Good match between simulation and measurement has been achieved. Models are used to improve RF and ruggedness performance in amplifier designs.
Microwave Integrated Circuits Conference, 2009. EuMIC 2009. European; 10/2009
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the high-temperature operation of confinement enhanced dots-in-a-well (CE-DWELL) quantum-dot infrared photodetectors (QDIPs). The thin Al<sub>0.3</sub>Ga<sub>0.7</sub>As barrier layer added above the InAs QDs greatly improve the lateral confinement of QD states in the In<sub>0.15</sub>Ga<sub>0.85</sub>As DWELL structure and the device performance. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature, and long-wavelength detection at the same time.
IEEE Photonics Technology Letters 02/2009; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A scalable nonlinear HBT model for a building block (1 BB) of 28 V InGaP/GaAs HBT is presented. It is based on the AgilentHBT (AHBT) model. The building block consists of 32 finger HBTs, an input pre-matching circuit and a transistor used as an emitter follower in the related bias circuit. The P1 dB of 1 BB is 32.5 dBm. The model can account not only for DC, thermal, junction capacitances, S-parameters but also RF power, gain, IM3, operation current and collector efficiency. A good match between simulation and measurement has been achieved. By using a multiplicity parameter the model can accurately predict the DC and nonlinear RF performance of two building blocks (64 fingers, P1 dB of 35.7 dBm) and four building blocks (128 fingers, P1dB of 38.2 dBm).
Microwave Symposium Digest, 2008 IEEE MTT-S International; 07/2008
-
[show abstract]
[hide abstract]
ABSTRACT: This paper reports on a 40 W high linearity InGaP/ GaAs 28 V HBT. It uses a high breakdown voltage, high ruggedness HBT process developed by WJ. The device employs a dynamic bias circuit to improve ACLR under WCDMA modulation conditions. The P-1 dB of the device reaches 46 dBm (40W), with a gain around 14.5 dB. With WCDMA one carrier modulation (PAR=8.5 dBc), the device achieves an ACLR of -50 dBC and an efficiency of 19.5% at an output power of 37.5 dBm (5.6 W) at 920-960 MHz frequency band. Without the help of a DPD, the performance of this device will make it an excellent choice for base station and repeater applications.
Microwave Symposium Digest, 2008 IEEE MTT-S International; 07/2008
-
[show abstract]
[hide abstract]
ABSTRACT: Nonlinear distortion of a power amplifier (PA) due to the nonlinear input-output transfer function is studied. The high-order nonlinearity or Fourier components of the output, due to the mixing of input signals, are found to be related to an average integral related to the transfer function, thus giving insight to the cancellation effect of the nonlinearity. A simple formula has been derived to relate the nth-order Fourier component of a nonlinear transfer function with a sinusoidal input to an average integral of the nth-order derivative of the transfer function. The large signal nonlinear distortion of the nth-order can therefore be regarded as a weighted average of the nth-order derivative of the transfer function. For PAs, the averaging effect gives rise to local minima in the intermodulation distortion terms during power sweep because of the cancellation of the positive part and the negative part of the derivative during averaging. We have applied the formula to InGaP heterojunction bipolar transistors PAs and are able to explain most of the observed nonlinear phenomena of the amplifiers.
Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2008; · 1.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The evolution of InAs quantum ring (QR) formation and the corresponding optical properties were investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. Just like a nanoscale volcanic eruption, the transformation from quantum dots (QDs) to QRs using the capping and annealing process depends on how much InAs is removed from the center of the dots to the surrounding areas. The final structure was found to depend on the annealing temperature and the cap layer thickness. We have investigated the QR formation at different stages using various growth conditions. The findings provided a clear picture on the mechanism of ring formation. We were able to obtain QRs with various geometries by controlling these growth parameters.
Journal of Applied Physics 07/2007; 102(2):024314-024314-5. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Distinct light emission peaks from monolayers of GaSb quantum wells in GaAs were observed. Discrete atomic layers of GaSb for the wetting layer prior to quantum dot formation give rise to transition peaks corresponding to quantum wells with 1, 2, and 3 ML. From the transition energies the authors were able to deduce the band offset parameter between GaSb and GaAs. By fitting the experimental data with the theoretical calculated result using an 8×8 k∙p Burt’s Hamiltonian along with the Bir-Picus deformation potentials, the strain-free (fully strained) valence band discontinuity for this type-II heterojunction was determined to be 0.45 eV (0.66 eV).
Applied Physics Letters 06/2007; 90(24):243102-243102-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper reports the device process and reliability aspects of a high voltage InGaP/GaAs HBT technology for 28V operation. The key differences and challenges from the material and process perspectives relative to the conventional low voltage HBT technology are first described. Long-term reliability tests performed at 28V bias voltage, 5.2kA/cm<sub>2</sub> current density and 310degC junction temperature resulted in zero device failures after over 3600 hours of stress. Wafer-level reliability tests using extreme current stress conditions were used to force transistors to degrade in short time for quick checking of transistor integrity and process reliability. Transistor lifetimes were generally higher than those in conventional low voltage HBTs at similar junction temperatures. Combining with the previously reported ruggedness and linearity performance, the high voltage InGaP/GaAs HBT is a mature technology for use in the 28V high linearity power amplification
Compound Semiconductor Integrated Circuit Symposium, 2006. CSIC 2006. IEEE; 12/2006
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we evaluate the two-tone intermodulation distortion for heterojunction bipolar transistors (HBTs) operated at RF. We directly solve the nonlinear differential equations of the HBT large-signal model in time domain by employing the waveform-relaxation and monotone-iterative methods. Based on time-domain results, sinusoidal waveform outputs are transformed into the frequency domain with the fast Fourier transform. Furthermore, the output third-order intercept-point values of the HBT are computed with the spectra. Results for a fabricated InGaP HBT under different testing conditions are reported and compared among the HSPICE results, the results with harmonic balance methodology, and the measured data. Comparisons among these results show that our method demonstrates its superiority over the conventional approaches. This characterization alternative has allowed us to study RF device properties, perform thermal consumption and sensitivity analysis, and extract model parameters.
IEEE Transactions on Microwave Theory and Techniques 11/2003; · 1.85 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Photoelectron relaxation in the second miniband of a superlattice was studied with a high-pass energy filter at one end of the superlattice. By analyzing the spectral responses with different biases across the energy filter, the photoelectron distribution and relaxation in the second miniband of the superlattice can be resolved. In this paper, a model based on the rate equation is proposed to extract the related parameters of the photoelectron transport. The photoelectrons suffer from both intraminiband and interminiband relaxation. The extracted interminiband relaxation time is 11 ps, while the intraminiband one is in the subpicosecond range. In addition, this structure can also be utilized as an infrared photodetector. Our analysis shows that the fast intraminiband relaxation is the dominant mechanism of the maximum achievable responsivity of the detector and the theoretical model not only provides the insight of the photoelectron transport in the superlattice miniband but also is useful for designing a superlattice infrared photodetector.
IEEE Journal of Quantum Electronics 03/2003; · 1.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, the influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 /spl mu/m without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6/spl sim/0.8 /spl mu/m between the emitter and the base of an InGaP HBT is required.
IEEE Electron Device Letters 11/2002; · 2.85 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The thermal stability of multifinger bipolar transistors has been
analyzed theoretically. Coupled equations are solved to study the onset
of instability and its dependence on the distributions of ballasting
resistors. Analytical expressions were derived for the emitter
ballasting distribution for optimum stable operation. Compared to
conventional methods with uniform ballasting, the optimized design can
significantly increase the stable operating current of the transistor.
An absolutely stable operating condition is also derived. At this
condition, the device never becomes unstable
IEEE Transactions on Electron Devices 06/2002; · 2.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The thermal stability of multifinger bipolar transistors has been
analyzed theoretically. Coupled equations are solved to study the onset
of instability and its dependence on the distributions of ballasting
resistors. We extended our previous work on the multiple-finger
transistor thermal stability from the simple coupled thermal-electrical
feedback equation to the more accurate I-V equation and taking the
temperature dependence of the thermal conductivity into consideration.
Transistors with three-fingers and N-fingers have been analyzed. Two
design procedures, uniform current design and uniform temperature
design, of the best ballasting resistor distribution for optimum thermal
stability operation were developed. Using these design flows, we can
design the best ballasting resistor needed for thermal stable operation
under the specified current level or specified junction
temperature
IEEE Transactions on Electron Devices 06/2002; · 2.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two-dimensional (2D) optical field distribution and the far-field patterns are analyzed for semiconductor lasers with small vertical beam divergence. The discrete spectral index method is used for the analysis and compared with other methods such as the effective index method. The discrete spectral index method is found to be much better in terms of accuracy and computation efficiency for the laser structures studied. Two laser structures with experimental counterparts are studied. The best beam aspect ratio (
Optical and Quantum Electronics 01/2002; 34(7):661-675. · 0.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have successfully developed a selective surface coating technique to control the modal behavior of the ion-implanted vertical-cavity surface-emitting laser (VCSEL). With selective deposition of a germanium coating by the lift-off process, we could spatially control the threshold gain condition of the VCSEL to support the single transverse mode. The threshold current is 7 mA and single transverse mode operation is maintained up to 1 mW. The method is simple and nondestructive compared with other techniques.
Japanese Journal of Applied Physics 02/2000; 40(2A):614. · 1.06 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We theoretically analyze 630-nm band GaInP-AlGaInP
tensile-strained quantum-well (QW) lasers with doping in the active
region. The radiative current can be significantly reduced by
introducing n-type doping in the active region. However, this advantage
is reduced by the increase of the leakage current. As a result, the
threshold current is reduced and the emission wavelength is shortened
for multiquantum-well (MQW) lasers by n-type doping. But for
single-quantum-well (SQW) lasers, because of the large increase of the
leakage current, the threshold current increases with n-type
doping
IEEE Journal of Quantum Electronics 10/1998; · 1.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have demonstrated a high-performance two-wavelength asymmetric
Fabry-Perot modulator (AFPM) by using a novel decoupled cavity design.
In this new design, the middle mirror supplies a back-mirror
reflectivity for the short-wavelength modulator and, at the same time, a
front-mirror reflectivity for the long-wavelength modulator. The front
mirror is designed to be transparent at the long wavelength and
reflective at the short wavelength to eliminate the interference between
the two modulators. With this decoupled cavity design, we greatly
simplified the matching requirement for the two cavities and obtain much
more flexibility in the device design. Experimentally, we have
demonstrated a two-wavelength modulator operated at 860 and 890 nm with
operating voltages of 3.4 and 6.2 V and reflectivity changes of 62% and
44%, respectively
IEEE Journal of Quantum Electronics 04/1998; · 1.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: By using highly doped InGaAs quantum wells, grating-free two color
quantum well infrared photodetectors with large normal incidence
responses have been demonstrated. These devices have comparable
performance as conventional QWIPs with surface gratings but without the
complexity of gratings. The TE absorption was found to be enhanced by
the use of the highly strained InGaAs quantum wells and the high doping
concentration in the wells. Two-color QWIPs have also demonstrated with
excellent performance
Solid-State and Integrated Circuit Technology, 1998. Proceedings. 1998 5th International Conference on; 02/1998
