Μm In0 Research Articles

Frequency Response of Barrier Type 2.6 µm In0.83 Ga0.17 As/In0.83 Al0.17 As Photodetectors on InP

Frequency Response of Barrier Type 2.6 µm In_0.83 Ga_0.17 As/In_0.83 Al_0.17 As Photodetectors on InP

Stepper-based Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As PHEMTs on a 3-inch InP substrate with record product of fT and Lg

We have fabricated and characterized Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As pseudomorphic high-electron-mobility-transistors (PHEMTs) on a 3-inch InP substrate. Stepper-based photo-lithography was used in all the process steps for device fabrication, aiming to miniaturize key device geometries, such as gate-to-source and gate-to-drain spacing. The fabricated device with Lg = 0.5 μm exhibits an excellent maximum transconductance (gm_max) of 1.9 S/mm at VDS = 1.5 V and an ON-resistance (RON) of below 0.4 Ω-mm. A high value of gm in our device leads to a fantastic combination of current-gain cut-off frequency (fT) of 120 GHz and maximum oscillation frequency (fmax) of 366 GHz at VDS = 0.8 V. These remarkable characteristics stem from the compact geometry design of the In0.52Al0.48As/In0.7Ga0.3As PHEMTs with LGS = LGD = 0.4 μm, coupled with an optimized gate recess process that yields tight control of side-recess spacing (Lside). More importantly, the product of fT and Lg in this work yields 60 GHz-μm which is the highest in any field-effect-transistor (FET) technology on any material system.

A versatile digitally-graded buffer structure for metamorphic device applications

Exploring more effective buffer schemes for mitigating dislocation deficiencies is the key technology towards higher performance metamorphic devices. Here we demonstrate a versatile metamorphic grading structure consisting of 38-period alternated multilayers of In0.52Al0.48As and In0.82Al0.18As on InP substrate, thicknesses of which in each period were gradually varied in opposite directions from 48.7 and 1.3 nm to 1.3 and 48.7 nm, respectively, akin to a digital alloy. Both preferentially dislocation nucleation and blocking of threading dislocation transmission are observed near the In0.82Al0.18As/In0.52Al0.48As interfaces, which help relax the strain and lower the residual defect density. A 2.6 μm In0.83Ga0.17As pin photodetector is fabricated on this pseudo-substrate, attaining a low dark current density of 2.9 × 10−6 A cm−2 and a high detectivity of 1.8 × 1010 cmHz1/2W−1 at room temperature, comparable with the states of the art that on linearly-graded buffer layers. These results indicate such digitally-graded buffer structures are promising for enhancing performances of metamorphic devices, and can be easily generalized to other lattice-mismatched material systems.

InGaP (GaInP) mesa p-i-n photodiodes for X-ray photon counting spectroscopy

In this paper, for the first time an InGaP (GaInP) photon counting X-ray photodiode has been developed and shown to be suitable for photon counting X-ray spectroscopy when coupled to a low-noise charge-sensitive preamplifier. The characterisation of two randomly selected 200 μm diameter and two randomly selected 400 μm diameter In0.5Ga0.5P p+-i-n+ mesa photodiodes is reported; the i-layer of the p+-i-n+ structure was 5 μm thick. At room temperature, and under illumination from an 55Fe radioisotope X-ray source, X-ray spectra were accumulated; the best spectrometer energy resolution (FWHM) achieved at 5.9 keV was 900 eV for the 200 μm In0.5Ga0.5P diameter devices at reverse biases above 5 V. System noise analysis was also carried out and the different noise contributions were computed.

Study on the performance of 2.6 µm In0.83Ga0.17As detector with different etch gases

In order to obtain a low-damage recipe in the ICP processing, ICP-induced damage using Cl2/CH4 etch gases in extended wavelength In0.83Ga0.17As detector materials was studied in this paper. The effect of ICP etching on In0.83Ga0.17As samples was characterized qualitatively by the photoluminescence (PL) technology. The etch damage of In0.83Ga0.17As samples was characterized quantitatively by the Transmission Line Model (TLM), current voltage (IV) measurement, signal and noise testing and the Fourier Transform Infrared Spectroscopy (FTIR) technologies. The results showed that the Cl2/CH4 etching processing could lead better detector performance than that Cl2/N2, such as a larger square resistance, a lower dark current, a lower noise voltage and a higher peak detectivity. The lower PL signal intensity and lower dark current could be attributed to the hydrogen decomposed by the CH4 etch gases in the plasma etching process. These hydrogen particles generated non-radiative recombination centers in inner materials to weaken the PL intensity and passivated dangling bond at the surface to reduce the dark current. The larger square resistance resulted from the lower etch damage. The lower dark current meant that the detectors have less dangling bonds and leakage channels.

Spectroscopic study of transparency current in mid-infrared quantum cascade lasers

We report measurements which give direct insight into the origins of the transparency current for λ ~5 µm In0.6Ga0.4As/In0.42Al0.58As quantum cascade lasers in the temperature range of 80-280 K. The transparency current values have been found from broadband transmission measurements through the laser waveguides under sub-threshold operating conditions. Two active region designs were compared. The active region of the first laser is based on double-LO-phonon relaxation approach, while the second device has only one lower level, without specially designed resonant LO-phonon assisted depopulation. It is shown that transparency current contributes more than 70% to the magnitude of threshold current at high temperatures for both designs.

A TCAD-based modeling of GaN/InGaN/Si solar cells

Theoretical efficiency potential of GaN/InGaN/cSi tandem solar cells is investigated using two-dimensional numerical computer simulation (i.e. technology-based computer aided design tool: TCAD). With double-junction GaN/InGaN/cSi tandem design, a conversion efficiency of 27% is achieved using a 1.0 µm In0.5Ga0.5N absorber of top cell over crystalline silicon (cSi) bottom cell. This efficiency is further improved to 29.0% with grading of the InxGa1−xN absorber layer close to the top heterointerface (p+-GaN/n−-InxGa1−xN) of the solar cell. A maximum conversion efficiency is obtained when the band discontinuity ratio (i.e. ΔEC:ΔEV) is set to 0.65:0.35. While efficiency remains approximately constant with moderate n-doping (up to 5 × 1016 cm−3) in the top InGaN absorber layer, sensitivity of the efficiency to the interface trap density and trap cross-section (when traps are located only at the heterointerfaces) shows degraded behavior with increasing trap density and trap cross-section. A temperature coefficient for open-circuit voltage (efficiency) of −0.15 (−1.72 × 10−3 °C−1), −0.09 (−0.95 × 10−3 °C−1) and −0.2 (−2.38 × 10−3 °C−1)%/°C for single heterojunction (SHJ), double-heterojunction (DHJ) and tandem-graded design is predicted from the numerical simulations.

Room-temperature operation of 3.6 μm In0.53Ga0.47As/Al0.48In0.52As quantum cascade laser sources based on intracavity second harmonic generation

We discuss a design of short-wavelength quantum cascade laser sources based on intracavity second harmonic generation. A passive heterostructure tailored for giant optical nonlinearity is integrated on top of an active region and patterned for quasiphase matching. We demonstrate operation of λ≈3.6 μm lattice-matched InGaAs/AlInAs/InP sources with approximately 6 μW of second-harmonic output at room temperature and conversion efficiency of approximately 130 μW/W2. Threshold current densities of devices with a nonlinear section were similar to that of the reference lasers without the nonlinear section.

Crack-free GaAs epitaxy on Si by using midpatterned growth: Application to Si-based wavelength-selective photodetector

A monolithically integrated wavelength-selective photodetector, which consists of an 11.86 μm thick GaAs-based Fabry–Pérot filter and a 3.84 μm thick InP-based p-i-n absorption structure (with a 0.3 μm In0.53Ga0.47As absorption layer), was grown on a Si substrate. A crack-free and high-quality epilayer with an area of 800×700 μm2 was obtained by using midpatterned growth and thermal-cycle annealing. Long dislocations running parallel to the GaAs/Si interface were formed by thermal annealing. This kind of dislocation may effectively alleviate the thermal stress across a large patterned area and be responsible for the crack-free epilayer. A photodetector with a spectral linewidth of 1.1 nm (full width at half maximum) and a quantum efficiency of 9.0% was demonstrated.

Dispersive gain and loss in midinfrared quantum cascade laser

We report the measurements of dispersive gain (simultaneous coexistence of gain and losses on a single intersubband transition) in a quantum cascade laser. Broadband transmission spectra through the waveguide of a λ∼4.7μm In0.53Ga0.47As∕AlAs0.56Sb0.44∕InP quantum cascade laser have been studied at a bias below laser threshold and at different temperatures. For a certain range of current, and at temperatures higher than about 150K, the transmission spectra show clear dispersive gain/loss behavior with the possibility for intersubband gain to be observed even without global population inversion between laser levels.

Waveguide optical losses in InGaAs∕AlAsSb quantum cascade laser

The authors present a technique for broadband study of the optical waveguides used for midinfrared quantum cascade lasers. This method allows insight into the waveguide properties and helps in improving the waveguide design. Using this method the waveguide losses in the whole range of waveguide transparency of about 1.8–9μm have been found for a λ∼4.4μm In0.53Ga0.47As∕AlAs0.56Sb0.44∕InP quantum cascade laser. The polarization dependence of waveguide losses in a quantum cascade laser is discussed.

Design and simulation of InGaAs∕AlAsSb quantum-cascade lasers for short wavelength emission

The design and simulation of an In0.53Ga0.47As∕Al0.56As0.44Sb quantum-cascade laser emitting in the near infrared is presented. Designed using a self-consistent rate equation solver coupled with an energy balance rate equation, the proposed laser has a calculated population inversion of ∼20% at 77K and sufficient gain to achieve room-temperature laser emission at λ∼2.8μm. Threshold currents in the range 4–8kA∕cm2 are estimated as the temperature increases from 77Kto300K. The output characteristics of the proposed laser are compared to an existing λ∼3.1μm In0.53Ga0.47As∕Al0.56As0.44Sb quantum-cascade structure presented in the literature.

Characteristics of MOCVD- and MBE-grown InGa(N)As VCSELs

We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) in the 1.3 µm range. The epitaxial structures were grown on (1 0 0) GaAs substrates by metalorganic chemical vapour deposition (MOCVD) or molecular beam epitaxy (MBE). The nitrogen composition of the InGa(N)As/GaAs quantum-well (QW) active region is 0–0.02. The long-wavelength (up to 1.3 µm) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE- and MOCVD-grown VCSELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In0.36Ga0.64N0.006As0.994/GaAs VCSELs. A very low Jth of 2.55 kA cm−2 was obtained for the InGaNAs/GaAs VCSELs. The MBE-grown devices were made with an intracavity structure. Top-emitting multi-mode 1.3 µm In0.35Ga0.65N0.02As0.98/GaAs VCSELs with 1 mW output power have been achieved under RT CW operation. A Jth of 1.52 kA cm−2 has been obtained for the MBE-grown In0.35Ga0.65N0.02As0.98/GaAs VCSELs, which is the lowest threshold current density reported. The emission characteristics of the InGaNAs/GaAs VCSELs were measured and analysed.

An Investigation of Direct-Current Characteristics of Composite-Emitter Heterojunction Bipolar Transistors

Direct-current characteristics of the composite-emitter heterojunction bipolar transistor (CEHBTs) having a composite emitter formed of a 0.04 µm In0.5Ga0.5P bulk layer and a 0.06 µm Al0.45Ga0.55As/GaAs digital graded superlattice (DGSL) were investigated. InGaP/DGSL-passivated and DGSL-passivated CEHBTs were fabricated for comparison with a AlGaAs-passivated CEHBT having an InGaP/AlGaAs emitter and a conventional InGaP/GaAs SHBT. In addition to having an extremely small collector–emitter offset voltage, the InGaP/DGSL-passivated and DGSL-passivated CEHBTs exhibit small base–emitter turn-on voltages, which are 130 and 370 mV lower than those of the InGaP/GaAs SHBT and comparison CEHBT, respectively, at a 1 A/cm2 collector current. These results reveal that the DGSL structure forms a gradedlike wide-gap emitter to effectively smooth out the potential spike at the base–emitter heterointerface. The current gain of the InGaP/DGSL-passivated CEHBT is 250 and is even enhanced to 385 by directly removing the InGaP layer. We qualitatively explain these improvements introducing the concept of a built-in electric field within the DGSL structure.

Compliant epitaxial growth of InxGa1−xAs and InxAl1−xAs on In0.25Ga0.75As pseudosubstrates

High-quality regrowth of InxGa1−xAs and In0.25Al0.75As layers on In0.25Ga0.75As pseudosubstrates was demonstrated. These pseudosubstrates were formed using lateral oxidation of an underlying Al0.98Ga0.02As layer to improve the material quality of a relaxed In0.25Ga0.75As seeding layer. Using transmission electron microscopy, dislocation densities in the regrown layers were measured and found to be equal to that of the underlying pseudosubstrates (⩽106 cm−2). Doping characterization of these regrown films, using Hall-effect measurements, was also performed for both Si-doped and Be-doped materials. The doped In0.25Ga0.75As films showed normal carrier concentration trends as compared to doped GaAs films and In0.53Ga0.47As films grown on InP substrates. The doped In0.25Al0.75As films, however, showed lower-carrier concentrations than expected. In addition, room-temperature photoluminescence (PL) measurements of thick (∼1 μm) In0.25Ga0.75As layers show emission near 1.1 μm indicating the high quality of the regrown material. Strained In0.40Ga0.60As quantum wells (QWs) were also grown in an In0.25Ga0.75As matrix. PL measurements taken at a temperature of 77 K show emission from the strained QWs at a wavelength near 1.23 μm. With further optimization, these materials promise room-temperature emission at wavelengths near 1.3 μm.

High Quality In1-x(Gax)AsyP1-y/InP Compressive Strained Quantum Well Structures Grown by LP-MOCVD

AbstractWe report the results of the growth of InAsyP1−y /InP and In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 compressive strained multiple quantum wells (CSMQW) structures grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Our studies showed high quality 1.06 μm InAs0.21P0.79/InP CSMQW structure with 6 periods can be obtained when the growth temperature is around 650°C and the pressure in the reactor is about 20 Torr. When the well thickness and composition are tuned for wavelength around 1.30 μm, the quality of this structure degrades. By employing 1.1 μm wavelength, lattice-matched InGaAsP as the barrier layers and setting the growth temperature at 600 °C, high quality 1.30 μm wavelength In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW materials with 10 periods can also be obtained. The materials were characterized with high resolution x-ray rocking curves, room and low temperature photoluminescence (PL). The 15K full-width-at-half-maximums (FWHM) of the PL peaks for 1.06 μm InAs0.21P0.79/InP and 1.30 μm In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW structures are 5.6 meV and 4.97 meV, respectively, which are among the smallest FWHMs reported up to date for these kinds of MOCVD growth materials. Buried heterostructure lasers at 1.3 μm wavelength have been obtained with the CSMQWs as the active layer.

The temperature dependence of threshold current of chemical beam epitaxy grown InGaAs–InP lasers

The temperature dependence of threshold current between 130 and 310 K of 1.65 μm In0.53Ga0.47As–InP bulk lasers grown by chemical beam epitaxy has been measured. Comparison with a calculation of the spontaneous recombination current at threshold allows one to determine the proportion of current loss over this temperature range. It is found that the loss can be described using an Auger recombination component of the form Rauger=C′n3 exp(−Ea/kBT) where n is the carrier population density in the undoped active region. The activation energy Ea is found to be 39±5 meV which is in excellent agreement with the theoretical value for the conduction to heavy hole band/split-off to heavy hole band Auger process. The values obtained for the Auger coefficient C over the temperature range are in close agreement with published values obtained by time resolved photoluminescence.

Gas source molecular beam epitaxy growth of ZnSe on novel buffer layers

Thin films of ZnSe on pseudomorphic and partially relaxed (In,Ga)P buffer layers (on GaAs) have been examined; both epilayers were grown by gas source molecular beam epitaxy. The ZnSe layers were grown using elemental Zn and thermally decomposed H2Se. The II–VI nucleation occurred following an ex situ transfer in air of the As-passivated (In,Ga)P buffer layers, grown using In, Ga, and cracked PH3. Microstructural characterization of the II–VI/III–V heterostructures was performed with high-resolution x-ray diffraction and transmission electron microscopy. The (511) reflection of the x-ray rocking curves was used to measure the residual strain in the ZnSe/(In,Ga)P/GaAs structures, and to determine the alloy composition of the (In,Ga)P. The (400) reflection of the x-ray diffraction rocking curves indicated peaks having full width at half-maximum of 130 and 18 arcsec for the relaxed ZnSe on thin (1 μm) pseudomorphic (In,Ga)P buffer layers, respectively. Transmission electron microscopy confirmed the relaxed or pseudomorphic nature of each heterolayer. Thicker (≳4 μm) In0.52Ga0.48P buffer layers were still not completely relaxed, and exhibited a residual lattice mismatch of approximately 0.11% between the ZnSe layer and the In0.52Ga0.48P buffer layer. Relatively thick (1–2 μm) ZnSe films had surface morphologies that were featureless when examined by Nomarski microscopy and scanning electron microscopy. Low-temperature photoluminescence spectra originating from the ZnSe films on the partially relaxed (In,Ga)P buffer layers were dominated by donor-bound and free-excitonic features with each exhibiting nearly the same intensity. Luminescence from extended defects (the Y0 and Iv transitions) within the ZnSe layer, and luminescence originating from the (In,Ga)P buffer layers, were also observed.

Molecular beam epitaxial growth and luminescence of InxGa1−xAs/InxAl1−xAs multiquantum wells on GaAs

This letter reports the successful molecular beam epitaxial growth of high-quality InxGa1−xAs/InxAl1−xAs directly on GaAs. In situ observation of dynamic high-energy electron diffraction oscillations during growth of InxGa1−xAs on GaAs indicates that the average cation migration rates are reduced due to the surface strain. By raising the growth temperature to enhance the migration rate and by using misoriented epitaxy to limit the propagation of threading and screw dislocations, we have grown device-quality In0.15Ga0.85As/In0.15Al0.85As multiquantum wells on GaAs with a 0.5–1.0 μm In0.15Ga0.85As buffer layer. The luminescence efficiency of the bound exciton peak increases with misorientation and its linewidth varies from 11 to 15 meV.

Analysis of Dark Currents and Minimum Detectable Powers for InGaAsP Optical Receivers

The dark current for 1.3 µm InGaAsP and In0.53Ga0.47As avalanche photodiodes was found to consist of two components: (1) a band-to-band tunneling current observed near the breakdown voltage and (2) a generation current at a lower bias voltage. An extensive estimation of the dark current for both diodes is made over a wide range of the donor density for epitaxial wafers on the basis of experimental results. Calculations of the minimum detectable power are made for InGaAsP optical receivers, including avalanche photodiodes and PIN diodes, as a function of various parameters according to the theory by Smith et al. A comparison between minimum detectable powers for avalanche photodiodes and PIN diodes reveals that for λ=1.3 µm, 1.3 µm InGaAsP avalanche photodiodes can provide a better sensitivity than In0.53Ga0.47As PIN diodes whereas for λ=1.5 µm, In0.53Ga0.47As PIN diodes can provide a sensitivity comparable to or better than In0.53Ga0.47As avalanche photodiodes.