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This paper provides a comprehensive study of the fiber dispersion effect for the generation of quasi-sinusoidal terahertz modulations on optical pulses, which are especially beneficial for the applications of terahertz photonic generation and low-frequency coherent Raman spectroscopy. Instead of compensating the fiber group-velocity dispersion in a fiber-delivery system, we propose to make a good use of this fiber dispersion effect, so as to simultaneously chirp and beat the optical pulses. We have not only derived the formulas, but also experimentally elucidated the dispersion effect on the generation of quasi-sinusoidal terahertz modulations via different fiber lengths. The maximum modulation frequency on top of an optical pulse was experimentally demonstrated up to 3.75 THz. To show its application, a low-temperature-grown gallium arsenide-based bow-tie photoconductive antenna was excited by the fiber-delivered light source, and the corresponding frequency quasi-continuous-wave terahertz photons were successfully excited. The generated terahertz frequency was linearly tunable from 0.1 to > 2.1 THz. The linewidth and the spectral intensity of the modulated optical pulses, as well as the impulse response and the bandwidth saturation effect of the antenna, were also experimentally and analytically investigated. Because the laser source can be readily decoupled from the terahertz emitting end due to fiber delivery, this optical fiber-delivered configuration possesses the advantages of simplicity and higher flexibility, which are, therefore, suitable for tabletop biomedical applications or even for clinical uses. The dispersion analysis in the present study is also beneficial for the future manipulation of terahertz radiation, such as the direct generation of chirped terahertz waves.

Growth of InGaSb/AlSb high hole mobility quantum well field effect transistors (QW FETs) on Si substrates with a step-graded GaAsSb metamorphic buffer layer by molecular beam epitaxy is explored. With an optimized growth temperature for the InGaSb/AlSb QW, hole mobility of 770 cm 2 /V s and 3060 cm 2 /V s have been achieved at room temperature and 77 K, respectively. It is also found that the twins in the samples do not cause significant anisotropic behavior of the InGaSb QW FETs in term of gate direction.

In this work, the InAs/AlSb high electron mobility transistors (HEMTs) on GaAs semi-insulating substrate using refractory iridium (Ir) gate technology was proposed. The Ir-gate exhibited a superior metal work function which was beneficial for increasing Schottky barrier height of InAs/AlSb heterostructures to 0.58 eV. Compared to the Ti-gate HEMT, the Ir-gate HEMT shows higher threshold voltage and lower gate leakage current owing to its higher Schottky barrier height and higher melting point. Moreover, the Ir-gated HEMT also shows the manifest stability improvement of DC characteristics under hot carrier stress as the Ti and As diffusion is alleviated.

Display Omitted The Ir-gate AlSb/InAs HEMT on Si substrate has been studied with reliability evaluation.The Ir-gate exhibited a superior metal work function.The Schottky barrier height of InAs/AlSb on silicon was improved.TEM, SIMS, and low frequency noise measurement were adopted to proof device stability. In this work, the 6-inch AlSb/InAs on Si (001) substrate is used to increase device integration and cost-effective purpose. The iridium (Ir)-gate was used for the InAs/AlSb on silicon substrate and temperature-dependent characteristics were also studied. The Ir-gate exhibited a superior metal work function which was beneficial for increasing the Schottky barrier height of InAs/AlSb on silicon heterostructures. Moreover, transmission electron microscopy, secondary ion mass spectrometry, and low frequency noise measurements were conducted to proof that the Ir-gated AlSb/InAs HEMT achieved the better stability of characteristics after self-heating and hot-carrier stresses.

We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb layer also provides a smoother surface morphology with its root mean square roughness of 0.664 nm. Using a GaAsSb step-graded buffer (SGB) and an AlGaAsSb high resistivity buffer, we are able to grow a 200 nm p-type InGaAs layer on Ge and yield hole mobility of 37.5 cm2/V-s at 300K and 53.1 cm2/V-s at 77K with hole concentration of 2.6×1019 cm−3 and 1.2×1019 cm−3, respectively.

This paper investigates terahertz (THz) wave propagation, resonance, and radiation on a THz optoelectronic integrated circuit (THz-OEIC). An efficient THz resonant radiation from 0.6 to 0.7 THz can be achieved with a newly designed 2-D open-ended rampart slot array antenna. A monolithically integrated circuit is fabricated on a localized THz resonant cavity, which not only provides a robust base for postdevice processes but also helps collect and reradiate the fleeing surface waves to enhance radiation efficiency. When using a THz time-domain spectroscopy (THz-TDS) technique and a time-frequency analysis, the radiated THz waveform shows a good time-frequency correlation to the circuit design of our THz-OEIC. In addition, an optical-to-THz per-pulse conversion efficiency of 6.41 × 10-3 can be achieved by a localized THz resonant cavity design. The enhanced optical-to-THz per-pulse conversion efficiency and THz propagation, resonance, and radiation behavior revealed not only help to understand the on-chip THz transmission phenomena but provide a good potentiality for a THz-OEIC design to be applied in low power-consuming microfluidic-channel-based THz biosensing chips as well.

Effects of thermal annealing on the emission properties of type-II InAs quantum dots (QDs) covered by a thin GaAs 1− x Sb x layer are investigated by photoluminescence (PL) and time-resolved PL measurements. Apart from large blueshifts and a pronounced narrowing of the QD emission peak, the annealing induced alloy intermixing also leads to enhanced radiative recombination rates and reduced localized states in the GaAs 1− x Sb x layer. We find that the type-II QD structure can sustain thermal annealing up to 850 °C. In particular, we find that it is possible to manipulate between type-I and type-II recombinations in annealed QDs by using different excitation powers. We demonstrate that postgrowth thermal annealing can be used to tailor the band alignment, the wave function overlaps, and hence the recombination dynamics in the InAs/GaAs 1− x Sb x type-II QDs.

Considerable on-state impact ionization and off-state tunneling leakages are the two principal drawbacks of InAs/AlSb HEMTs, which have a small bandgap and type-II band lineup. This work introduced a wide-bandgap high-k Al2O3 between the gate metal and semiconductor surface and successfully demonstrated DC and RF performance of the InAs/AlSb metal–oxide–semiconductor HEMTs (MOS-HEMTs). An MOS-HEMT device with a 2.0 μm gate length yields DC performance of IDSS = 286 mA/mm and Gm = 495 mS/mm and RF performance of fT = 10.1 GHz and fMAX = 19.9 GHz. Compared with a conventional HEMT, gate leakage is reduced by one order and the marked dependence of drain current on gate bias in the deep subthreshold region is largely alleviated.

Conventional InAs/AlSb HEMTs suffer from chemical instability in materials and high kink current. To avoid these drawbacks, this work proposes a novel layer structure of an InAsSb/AlSb HEMT and a novel two-step passivation process. Performance improvements are reduced dc output conductance by approximately 4.6 times at V DS = 0.5 V and I D = 100 mA/mm, and gate leakage to 1 × 10 −3 mA/mm from 4 at V GS = −1.2 V and V DS = 0.8 V compared with those of two InAs/AlSb HEMTs, one with the conventional one-step and the other with the proposed two-step passivation process. Both dc and rf performances show strong evidences of impact ionization suppression.

The effects of InGaAsSb and InAlAsSb strain-reducing layers on the optical properties of InAs/GaAs QDs are investigated. With these Sb-containing overgrown layers, InAs QDs exhibit much enhanced photoluminescence efficiency and thermal stability in the wavelength of 1.3 um and above, which is essential for long wavelength photonic devices.

We report the preparation of low density self-assembled InGaAs on GaAs grown by metal–organic chemical vapour deposition for single photon sources. Through using a set of optimized growth parameters, including the arsine partial pressure, total coverage of quantum dots, and growth temperature, high optical quality quantum dots with density as low as 5 × 106 cm−2 have been obtained. Using local optical excitation through a sub-micron aperture of a single quantum dot, its spectral lines associated with the exciton, biexciton, multi-exciton, and charged exciton have been resolved and identified. Photon correlation measurements show that the single quantum dot can successfully emit antibunched photons.

This letter reports the effect of growth temperature on carrier transport characteristics in In0.4Ga0.6Sb/AlSb heterostructure and demonstrates that hole mobility was enhanced by eliminating a parallel conducting channel in the buffer layers. Based on optimized growth conditions, hole mobility as high as 1220 cm2/V·s with carrier concentration of 1.3 ×1012 cm-2 was achieved. A 0.2- μm-gate-length In0.4Ga0.6Sb/AlSb p-channel device exhibited a maximum drain current of 102 mA/mm, a peak transconductance of 92 mS/mm, and an on-state breakdown voltage over 3 V. The pinchoff was observed for a gate bias of 0.6 V at drain current of 1 mA/mm. The current-gain and power-gain cutoff frequencies were 15 and 20 GHz, respectively.

Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.

In this study, we investigate the directivity of the terahertz (THz) radiation pattern from a newly designed two-dimensional rampart slot array antenna integrated in an edge-coupled membrane photonic transmitter. The antenna design is based on the array theory which is well-developed in the microwave regime. By means of the array arrangement of rampart slot antennas, we demonstrate that the 3-dB beam width of the THz radiation pattern at 907 GHz is successfully confined within 30 in both and planes.

We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb barrier layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb barrier layer also results in a smoother surface morphology with its root-mean-square roughness of 0.7 nm due to the surfactant effect of Sb. Using a step-graded GaAsSb and AlGaAsSb metamorphic buffer layer, a 200-nm p-type In0.53Ga0.47As layer grown on Ge exhibits a hole mobility of 38 cm2 V−1 s−1 with a hole concentration of 2.6 × 1019 cm−3 at 300 K and 53 cm2 V−1 s−1 with a hole concentration of 1.2 × 1019 cm−3 at 77 K.

Antimonide-based heterostructural p-channel HFET epitaxies consisting of an In 0.44 Ga 0.56 Sb quantum well located between AlSb barriers were developed by molecular beam epitaxy. The In 0.44 Ga 0.56 Sb channel layer was compressively strained to enhance hole mobility. Room-temperature Hall measurements to the as-grown materials exhibited a hole mobility as high as 895 cm2/V s. Ti/Pt/Au and Pt/Ti/Pt/Au metals were utilized in Schottky gate metallization processes for evaluating their effects on the device performance. Considering the diffusivity of Pt metals, the devices with as-deposited and annealed Pt-based gates were characterized simultaneously and compared with the ones with Ti-based gates. The devices with Ti-based gates yielded superior dc and rf performances to those with Pt-based gates.

In this work, N+-InGaAs/InAlAs recessed gates for InAs/AlSb HFET development are presented. Highly doped N+-InGaAs cap layers are used to decrease the parasitic resistances in contact and access regions. As-grown modulation-doped epitaxy materials exhibit a Hall mobility of 14,200 cm2/V s and a sheet density of 6.15 ×1012 cm−2, while a mobility of 14,600 cm2/V s and a sheet density of 5.61×1012 cm−2 are shown after removal of the N+-InGaAs cap. Benefiting the energy band lowering using the highly doped cap layers, a low contact resistance of 0.06 Ω-mm is achieved. DC performances of I DSS =862mA/mm and g m, peak =927mS/mm and RF performances of f T =24GHz and f max =51GHz are demonstrated in a 2.1μm-gate-length device. An f T -L g product is as high as 51 GH-μm.

Small-bandgap InAs channel materials are potential candidates for high-speed and low-power applications and have been demonstrated in AlSb/InAs/AlSb QWFETs. Taking advantage of their excellent transport properties, we successfully develop an InAs-channel metal-oxide-semiconductor modulation-doped field-effect transistor (MOS-MODFET) using 100-nm PECVD-deposited SiO 2 dielectrics for gate dielectrics. A 2µm-gate-length depletion-mode InAs n-channel MOS-MODFET shows a maximum drain current of 270 mA/mm, a peak transconductance of 189 mS/mm, and a low output conductance of 18 mS/mm in dc characteristics, and a maximum current-gain cut-off frequency of 14.5 GHz and a maximum oscillation frequency of 24.0 GHz in rf performances. The InAs-channel MOS-MODFET presents potentials for further developing complementary circuit devices.

We propose to integrate a high-gain open-ended rampart slot array antenna in our edge-coupled terahertz (THz) photonic transmitters. By locating the open circuits at the end of each quarter-wavelength slot antenna, the reflected terahertz wave can constructively interference with the input wave and hence produce higher gain. In addition, the folded feeding networks turn more propagating waves into the effective radiating segments rather than the dispersive surface waves. A THz resonant cavity is also designed under our monolithic THz-wave circuits. A 300-nm gold layer is coated below the substrate to serve as a reflecting mirror to reflect back the THz waves to the antenna. The resonant cavity design not only provides a robust base for post device process but also greatly enhances the gain of antenna. With the design of openended rampart slot array antenna and THz resonant cavity, we demonstrate that the gain of antenna can reach 8~9 dBi.

We successfully demonstrated DC and RF performance of a metal-oxide-HEMT based on baseline InAs/AlSb HEMT epitaxy material. E-beam evaporated Al 1−x O x was chosen for the dielectric film and its composition characterized by EDS. In a device with 2.0µm gate length, maximum drain current is 286mA/mm and peak transconductance is 495mS/mm at drain voltage of 0.4V. Microwave performance shows a ƒ T of 10 GHz and an ƒ max of 20 GHz. Degraded subthreshold slope but suppressed gate leakage specifically at large electric field were observed.

In recent years, the theories and technologies of optically pump photonic crystal (PC) devices, such as PC lasers and single photon sources, have been investigated extensively. However, progress on electrically driven PC devices has not been as successful. In 2004, Park et al. demonstrate an electrically driven PC laser, which has a sub-micrometer semiconductor post at the center of the single cell PC cavity [1]. The central post acts as an electrical conduction channel as well as a heat sinker nicely. On the other hand, to achieve efficient PC devices, such as lasers and single photon sources, PC cavities with not only high Q values but also small mode-volumes (V m ) are necessary. Among the reported PC cavities, L3 cavity, modified-H1 cavity, and quasi-L2 (qL2) cavity are good candidates for realizing high efficiency PC devices [2∼4]. Both the L3 and modified-H1 cavities provide a central mode with very high Q values while the qL2 cavity has a dipole mode with an extremely small mode-volume (∼0.019 µm3) at the central region. Therefore, the characteristics of the aforementioned PC cavities would suffer from the presence of the central post in terms of mode confinement and integrity. In this work, we propose an oxygen-ion implantation method to replace the central post. An electrically driven InAs quantum dot (QDs) light-emitting diode with qL2 PC cavity is demonstrated.

Conventional InAs/AlSb HEMTs suffer high gate leakage and incomplete pinch-off issues due to instable chemical property of the AlSb and GaSb materials though their excellent performance and circuit application have already been demonstrated. Based on the concerns, we proposed a two-step passivation process for minimizing the negative effect based on developed high-quality InAs/AlSb HEMT materials by solid-source molecular beam epitaxy. Improved device performance is observed.

We design and realize a single mode qL2 photonic crystal defect cavity near the 1.3 µm band. Taking advantage of its small mode volume, 1.3 µm InAs quantum dot light emitters with this cavity exhibit an emission intensity as high as 70 times over the ones without it.

Growth, fabrication, and characterization for a type II lineup InAs/AlSb HFET are presented. An as-grown epitaxy wafer with a 300 K mobility of 21,300 cm2/V-s and an electron sheet concentration of 1.4times1012 cm-2 was processed into devices. Peak transconductance of 720 mS/mm and drain current of 650 mA/mm at drain voltage of 1.0 V are achieved in a 1-mum gate length device. It is observed strong drain bias dependence of both DC drain currents and transconductances, on-state bell-shaped peaks in the gate leakage, and a large dispersion between DC and RF transconductances. Strong impact ionization along with no hole confinement in the InAs channel are suggested attributions for these phenomena.

By adopting a novel CPW-fed rampart slot array antenna, we demonstrate a compact highly-directed THz photonic transmitter with a single photodetector source. 3dB radiation beam widths in both E- and H-planes are significantly reduced.

The effects of a thin InAlAsSb strain-reducing layer (SRL) on the optical properties of InAs/GaAs quantum dots (QDs) are studied. The adoption of the InAlAsSb SRL results in higher emission intensity and better size uniformity than its InAlAs counterpart. InAs QDs capped with the InAlAsSb SRL reveal a large state separation of 103 meV and thermal activation energy of 530 meV. The increase in radiative efficiency and temperature stability is attributed to high carrier confinement and reduced defects by the InAlAsSb SRL.

The optical properties of InGaAsN QW grown on AlGaAs/GaAs cladding layers have been investigated. Al contamination in the quantum well due to memory effect should be the root cause for the degradation of optical quality. We not only use proposed two-step growth but demonstrate a new method for reducing the Al contamination by growth interruption with DMHy. This approach shows good optical properties as well as two-step growth and more economic compared to the reported ones.

This reported work investigates InGaSb/AlSb p-channel HFETs with hydrogen plasma treatment. The study found that hydrogen plasma treatment can effectively shift threshold voltage from 0.47 to 0 V. A 0.2 µm gate-length device exhibited DC performances of a maximum drain current of 61 mA/mm, and a peak gm of 83 mS/mm.

A GaAsSb step-graded metamorphic buffer layer is used for growing InAs/AlSb high electron mobility transistor structures on Si substrate by molecular beam epitaxy. The step-graded metamorphic buffer layer effectively reduces the number of microtwins and stacking faults penetrating to the InAs channel as evidenced by transmission electron microscopy. By reducing the planar defects with the metamorphic buffer layer, a significant improvement on electron mobility up to 18 100 cm2/V s and 39 700 cm2/V s at room temperature and 77 K, respectively, is achieved.

We investigate the optical properties of InAs quantum dots (QDs) capped with a thin AlxGa1−xAsSb layer. As evidenced from power-dependent and time-resolved photoluminescence (PL) measurements, the GaAsSb-capped QDs with type-II band alignment can be changed to type-I by adding Al into the GaAsSb capping layer. The evolution of band alignment with the Al content in the AlGaAsSb capping layer has also been confirmed by theoretical calculations based on 8-band k⋅p model. The PL thermal stability and the room temperature PL efficiency are also improved by AlGaAsSb capping. We demonstrate that using the quaternary AlGaAsSb can take the advantages of GaAsSb capping layer on the InAs QDs while retaining a type-I band alignment for applications in long-wavelength light emitters.

InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd2O3 2–3 monolayers thick followed by an Al2O3 cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al2O3/MBE-Gd2O3/InAs and ALD-Al2O3/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔEc) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al2O3/InAs were determined, respectively. The insertion of a Gd2O3 layer increases the value of ΔEc by nearly 0.1 eV as compared to the case for Al2O3 directly deposited on InAs. The distribution of interfacial density of states (Dit) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low Dit value of 1012 cm−2 eV−1 near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drai...

The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime are found to be correlated with the capping layer thicknesses. Theoretical calculations indicate that the quantum confinement and the wave function distribution of hole states are sensitive to the GaAsSb capping layer thickness. The Sb induced change in QD size also plays a role in the optical properties of GaAsSb-capped QDs. Controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications. V C 2011 American Institute of Physics.

This study investigates the photoluminescence for self-assembled InAs quantum dots embedded in photonic crystal nanocavities as two of the air holes nearest the H1 cavity were shifted. A rapid decrease of resonant wavelength and quality factor for the cavity modes, in which the electric field patterns extended in the shifting direction, were found as the shift increased from 0.2 to 0.4 lattice constants. This phenomenon is interpreted as being caused by the formation of two point defects between the nearest and second nearest air holes.

We report the effects of thermal annealing on the emission properties of type-II InAs quantum dots (QDs) covered by a thin GaAs1−xSbx layer. Apart from large blueshifts and a pronounced narrowing of the QD emission peak, the annealing induced alloy intermixing also leads to enhanced radiative recombination rates and reduced localized states in the GaAsSb layer. Evidences of the evolution from type-II to type-I band alignments are obtained from time-resolved and power-dependent photoluminescence measurements. We demonstrate that postgrowth thermal annealing can be used to tailor the band alignment, the wave function overlaps, and hence the recombination dynamics in the InAs/GaAsSb type-II QDs.

The optical properties of InAs quantum dots (QDs) with a GaAs, an InAlAs, or an InAlAsSb overgrown layer are studied. For the InAs QDs with an InAlAsSb overgrown layer, their room temperature photoluminescence intensity is enhanced by as much as 4.5-fold compared to that of the QDs with an InAlAs one while maintaining similar narrow linewidth (26meV) and large ground-to first excited-state separation (103meV). The increase in radiative efficiency of the InAs∕InAlAsSb heterostructure is attributed to its better material quality due to the surfactant nature of Sb adatoms.

The authors report an effective way to enhance the optical efficiency of InAs quantum dots (QDs) on GaAs emitting at the wavelength of 1.5μm. It is found that the loss of holes from QDs to their proximity via the high indium composition InGaAs overgrown layer, which is necessary for achieving long wavelength emission, is the origin of photoluminescence intensity degradation at high temperature. Inserting a 4nm thick Al0.45Ga0.55As layer, acting as a carrier blocking layer, into the GaAs capping matrix can improve the room temperature photoluminescence peak intensity by five and two times for the ground and first excited states, respectively.

We report a comparative study on the growth of InAs quantum dots (QDs) on GaAs by metalorganic chemical vapor deposition using triethylgallium (TEGa) and trimethylgallium (TMGa) for the GaAs cap layer. QDs exhibit 1.3μm photoluminescence (PL) at room temperature, as the GaAs cap layer is directly grown on the QDs. The PL emission can be extended to 1.49μm when an In0.25Ga0.75As overgrown layer is inserted between the cap layer and the InAs QDs. The use of TMGa or TEGa for the growth of the GaAs cap layer is essential for a further increase in the emission wavelength of the InAs QDs. Strong PL emission at 1.55μm with a linewidth of 28meV can be obtained as the GaAs cap layer is grown by TEGa, while the optical properties degrade severely when using TMGa.

The optical properties of InGaAsN QW grown on AlGaAs∕GaAs cladding layers were investigated. Al contamination in the quantum well due to the memory effect is responsible for the degradation of optical quality. We propose a growth method to reduce the Al contamination by growth interruption and dimethylhydrazine passivation. This approach improves the optical properties as well as simplifies the growth processes significantly as compared to the reported methods.

We report selective growth of InAs self-assembled quantum dots (QDs) on nano-ridges (30–50nm) formed by wet chemical etching and epitaxial growth processes. The QDs formed on the ridges exhibit distinctive characteristics from those on the planar region between the ridges in terms of physical shape as well as optical property. The QDs, which align one by one on the top of the ridges, are of an asymmetric shape along the [011] and [011] directions. By defining the width of ridge and the monolayers of QDs, we are able to control the height and the width of these QDs. Compared to the QDs on the planar region between the ridges, the luminescence from QDs on the ridges exhibits a shorter wavelength, which is attributed to higher compressive strain in these QDs.