InP Substrates Research Articles

Thermally induced metastability of InGaAs single-layer for highly strained superlattices by metal-organic chemical vapor deposition

In this study, the metastability of In0.68Ga0.32As layers on InP substrates was investigated at various growth temperatures. The thickness of each metastable In0.68Ga0.32As layer was 40 nm, which is four times the critical thickness of the stable lattice with a stress of approximately 1%. The surface morphologies and roughness of the metastable In0.68Ga0.32As layers were highly sensitive to the growth conditions. Cross-hatches were observed on their surfaces when they were grown at various growth temperatures, and over this range, the surface roughness varied from 0.11 nm to 0.16 nm. The lowest surface roughness of 0.11 nm was achieved at 770 °C, and the metastable In0.68Ga0.32As layer showed a flat surface morphology with terraces parallel to the step edges. These results corresponded to those of the strain relaxation analysis of the metastable In0.68Ga0.32As layers using X-ray diffraction spectra. The In0.68Ga0.32As layer grown at 770 °C was almost fully strained, whereas those grown at other growth temperatures were relieved by approximately 10%. The flat surface morphologies and almost fully strained lattices suggested that the growth conditions were suitable for preparing high-quality superlattices with well-defined interfaces. The intuitive results of the metastable In0.68Ga0.32As single layers were utilized to grow high-quality In0.67Ga0.33As/Al0.64In0.36As superlattices with a reduction in the misfit dislocation by 41.8%. The results obtained herein suggest that the growth conditions for superlattices can be easily and efficiently optimized using the metastability of the materials.

Random alloy thick AlGaAsSb avalanche photodiodes on InP substrates

We demonstrate low noise random alloy (RA) Al0.85Ga0.15AsSb (hereafter AlGaAsSb) avalanche photodiodes (APDs) nearly lattice-matched to InP substrates. In contrast to digital alloy (DA), RAs are manufacturable due to the ease of growth. The 910 nm-thick RA AlGaAsSb was grown at a low temperature around 450 °C to mitigate phase separation by suppressing surface mobility of adatoms. The high quality of the RA AlGaAsSb material was verified by x-ray diffraction, Nomarski, and atomic force microscope images. Capacitance–voltage measurement found that the background doping concentration was 6–7 × 1014 cm−3, indicating very low impurity density in the RA AlGaAsSb material. Current–voltage measurements were carried out under dark condition and 455 nm laser illumination at room temperature. The breakdown occurs at −58 V. The dark current density at a gain of 10 was found to be 70 μA/cm2. This value is three orders of magnitude lower than previously reported DA AlAs0.56Sb0.44 APDs [Yi et al., Nat. Photonics 13, 683 (2019)], one order of magnitude lower than DA AlGaAsSb [Lee et al., Appl. Phys. Lett. 118, 081106 (2021)], and comparable to RA AlInAsSb APDs [Kodati et al., Appl. Phys. Lett. 118, 091101 (2021)]. In addition, the measured excess noise shows a low k (the ratio of impact ionization coefficients) of 0.01. These noise characteristics make the RA AlGaAsSb multiplier suitable for commercial applications, such as optical communication and LiDAR systems.

Tuning of circular photogalvanic effect of surface states in the topological insulator Sb2Te3 via structural deformation

Strain is a useful method to manipulate properties of three-dimensional (3D) topological insulators (TIs). In this study, we demonstrate the possibility to tune the circular photogalvanic effect (CPGE) of surface states of 3D TI Sb2Te3 films by applying external strain. The CPGE of 3D TI Sb2Te3 grown on SrTiO3 (STO) with different thicknesses has been systematically investigated. It is found that as the thickness of Sb2Te3 films increases from 7-quintuple layer (QL) to 27-QL, the CPGE current first increases and then decreases. Additionally, the CPGE currents demonstrate remarkable temperature dependence, which even reverse sign when the temperature is increased from 77 to 300 K. This phenomenon is due to the vertical thermoelectric effect and inverse spin Hall effect. Finally, the CPGE measurements of Sb2Te3 films under different mechanical strains are performed, and it is found that the CPGE current linearly decreases with the increase in the external strain. The variation in the CPGE current can be tuned up to 11% and 44% in the 18- and 12-QL Sb2Te3 grown on STO substrates under a tensile strain of 0.0225 and 0.0066, respectively. In particular, it can even reach 100% in the 30-QL Sb2Te3 film grown on an InP substrate under a tensile strain of 0.0033, which is due to the combined effect of mechanical deformation and spin injection from substrates. Our work provides a method to effectively manipulate the CPGE in 3D TIs by the combined effect of mechanical strain and spin injection from substrates, which paves the way for novel opto-spintronic devices.

Responsibility optimization of a high-speed InP/InGaAs photodetector with a back reflector structure.

Top-illuminated PIN photodetectors (PDs) are widely utilized in telecommunication systems, and more efforts have been focused on optimizing the optical responsibility and bandwidth for high-speed and capacity applications. In this work, we develop an integrated top-illuminated InP/InGaAs PIN PD with a back reflector by using a microtransfer printing (µ-TP) process. An improved µ-TP process, where the tether of silicon nitride instead of photoresist, is selected to support an underetched III-V device on an InP substrate before transfer. According to theoretical simulations and experimental measurements, the seamless integration of the PD with a back reflector through µ-TP process makes full use of the 2nd or even multiple reflecting light in the absorption layer to optimize the maximum responsibility. The integrated device with a 5 µm square p-mesa possesses a high optical responsibility of 0.78 A/W and 3 dB bandwidth of 54 GHz using a 500 nm i-InGaAs absorption layer. The present approach for top-illuminated PIN PDs demonstrates an advanced route in which a thin intrinsic layer is available for application in high-performance systems.

Gain-switching of 1.55 µm InP-based Qdash lasers grown on Si

Reliable lasers on Si with large bandwidth are desirable for high-performance data communication systems on Si-photonics platforms. Here, we report short optical pulses generated by gain-switched InP-based 1.55 µm quantum dash (Qdash) lasers directly grown on (001) Si. The laser performance and related physical parameters were investigated by carrying out a gain-switching test for lasers on both Si and native InP substrates. The shortest pulses obtained were 217 and 252 ps for the lasers on InP and Si, respectively. By varying the electrical bias and pulse duration systematically, the evolution of the generated optical pulse duration and peak power was studied. The impact of cavity size on the optical pulse was also examined. Parameters were extracted using established equations fitted with our measurement results to gain insight into the underlying physics and correlation with the observed behavior. The obtained results indicate that the pulse width is limited by the low differential gain and strong gain compression of the active material. Our results indicate that Qdash lasers on Si can demonstrate comparable performance to those on a native InP substrate and manifest its potential application in an Si-based photonics chip for optical on-chip communications.

Droplet epitaxy symmetric InAs/InP quantum dots for quantum emission in the third telecom window: morphology, optical and electronic properties

Abstract The rapidly developing quantum communication technology requires deterministic quantum emitters that can generate single photons and entangled photon pairs in the third telecom window, in order to be compatible with existing optical fiber networks and on-chip silicon photonic processors. InAs/InP quantum dots (QDs) are among the leading candidates for this purpose, due to their high emission efficiency in the required spectral range. However, fabricating versatile InAs/InP QD-based quantum emitters is challenging, especially as these QDs typically have asymmetric profiles in the growth plane, resulting in a substantial bright-exciton fine structure splitting (FSS). This hinders the generation of entangled photon pairs and thus, compromises the versatility of InAs/InP QDs. We overcome this by implementing droplet epitaxy (DE) synthesis of low surface density (2.8 × 108 cm−2) InAs x P1−x QDs with x = (80 ± 15)% on an (001)-oriented InP substrate. The resulting QDs are located in etched pits, have concave bases, and most importantly, have symmetric in-plane profiles. We provide an analytical model to explain the kinetics of pit formation and QD base shape modification. Our theoretical calculations of electronic states reveal the properties of neutral and charged excitons and biexcitons confined in such QDs, which agree with the optical investigations of individual QDs. The optical response of QDs' ensemble suggests that FSS may indeed be negligible, as reflected in the vanishing degree of linear polarization. However, single QD spectrum gathered from an etched mesa shows moderate FSS of (50 ± 5) µeV that we link to destructive changes made in the QD environment during the post-growth processing. Finally, we show that the studied DE QDs provide a close-to-ideal single-photon emission purity of (92.5 ± 7.5)% in the third telecom window.

Monolithic two-color short-wavelength InGaAs infrared photodetectors using InAsP metamorphic buffers

A bias-selectable two-color heterojunction bandgap engineered InGaAs thin film infrared photodetector, monolithically grown on an InP substrate by metal–organic chemical vapor deposition, is demonstrated. The detector structure has two back-to-back diodes, with In0.53Ga0.47As and In0.83Ga0.17As absorbers separated by n+-InAsxP1-x metamorphic buffers to accommodate for the lattice mismatch between the absorbers of ∼2%. The surface of the topmost metamorphic buffer of InAs0.63P0.37, acting as a lattice-matched virtual substrate for the In0.83Ga0.17As absorber, has a Gaussian height distribution with a low surface roughness of 2.8 nm. The InAsxP1-x buffers achieve a gradual lattice constant transition from In0.53Ga0.47As to In0.83Ga0.17As, with a sufficient strain relaxation of 97%. Compared to the In0.53Ga0.47As diode, the In0.83Ga0.17As diode shows a higher reverse saturation current density by a factor of approximately 104, owing to a shorter minority carrier lifetime and a higher intrinsic carrier concentration. The bias-dependent two-color detection at the cutoff wavelengths of 1.7 μm and 2.6 μm is achieved, enabled by the In0.53Ga0.47As (blue channel) and In0.83Ga0.17As (red channel) absorption, respectively. The two-color InGaAs photodetector exhibits high specific detectivities of 4.1×1011 and 3.1×109 cm·Hz1/2/W at 300 K in both the blue and red channel regions, respectively.

InP and InGaAs grown on InP substrate by molecular beam epitaxy

InP and InGaAs epitaxial layers on InP substrates using molecular beam epitaxy (MBE) have been studied. Carrier concentration and mobility of InP and InGaAs are found that are strongly correlated with the growth temperature and V/III ratio. The InGaAs layers using As2were compared with the layers grown using As4from a Riber standard cracker cell. When As4is used, the highest electron mobility of InGaAs is 3960 cm2/(V·s) with the V/III ratio of 65. When converted to As2, the V/III ratio with the highest electron mobility decreased to 20. With the arsenic cracker temperature decreased from 950 ℃ to 830 ℃, the electron mobility increased from 4090 cm2/(V • s) to 5060 cm2/(V • s).

Heterogeneously integrated membrane III-V compound semiconductor devices with silicon photonics platform

Silicon photonics is a key technology for constructing large-scale photonic integrated circuits (PICs) because it enables large-scale wafer processes with high uniformity and quality. To further improve device characteristics, heterogeneous integration of III-V compound semiconductors that provide optical gain, a high modulation efficiency, and optical non-linearity is desired. This paper describes the heterogeneous integration of membrane III-V compound semiconductor photonic devices that have a similar structure including thickness and refractive index. These devices provide efficient optical coupling with a Si waveguide using a simple taper waveguide structure. If the total thickness of the film structure is designed to be less than the critical thickness (calculated to be 430 nm for fabrication conditions such as bonding and growth temperatures), high-quality epitaxial layers can be grown on a thin InP layer directly bonded to the Si substrate. Therefore, regrowth techniques are employed on bonded InP layer on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si substrate. We fabricate two kinds of laser-integrated Mach-Zehnder modulators using epitaxial regrowth on Si substrates. One uses Si phase modulators, and the other uses InP-based modulators. A micro-transfer-printing technology is also important when the number of III-V devices is relatively small. Furthermore, the micro-transfer-printing technology enables devices to be selected that meet the required characteristics before integration. For this purpose, we try to integrate a membrane laser on a Si substrate, in which the membrane laser is fabricated on InP substrate. The device shows a threshold current of 0.8 mA when the active region length is 140 μm. Finally, we briefly describe a transmission module, in which directly modulated membrane lasers and electronic drivers are integrated by flip-chip bonding through Au bumps. To reduce power consumption, it is important to design driver circuits that incorporate semiconductor lasers as electronic components. We demonstrate a 2-channel 53-Gbit/s 4-level pulse amplitude modulation (PAM4) transmitter front-end consisting of a 2-channel PAM4 shunt laser driver and 2-channel O-band directly modulated membrane lasers. The total power consumption is only 60.7 mW, resulting in 0.57 mW/Gbit/s.

Inverted metamorphic InGaAsP/InGaAs dual-junction solar cells towards full solar spectrum harvesting

An InGaAsP (1.04 eV)/InGaAs (0.54 eV) dual-junction solar cell, monolithically grown in an inverted configuration on an InP substrate, has been demonstrated.

H-Band Broadband Balanced Power Amplifier in 250-nm InP HBT Technology Using Impedance-Transforming Balun

A broadband power amplifier in a 250-nm InP HBT technology is presented, working at full <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -band (220–320 GHz). A cascode transistor is employed as a power cell to achieve high gain and power at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -band. Two-stage cascode power amplifier is designed with input and output impedance of not 50 but 25 Ω, reducing the impedance transformation ratio and allowing the broadband matching networks. Two power-amplifier channels are power-combined using on-chip baluns which performs the impedance transformation from 25 to 50 Ω. The balun operation is based on the electromagnetic field conversion between coplanar waveguide and microstrip line. It does not rely on long transmission lines with frequency-dependent length, so that it occupies a very compact area and exhibits a broadband performance. It also enables power amplifiers to operate in the balanced mode, allowing the area reduction and stable operation. Substrate modes and in-band resonances in InP substrate, which seriously degrade circuit performance and limits bandwidth, are effectively suppressed by the reduced on-chip ground and balanced operation. The fabricated power amplifier shows a measured small-signal gain of 20.8 dB at 232 GHz with a 3-dB bandwidth larger than 51 GHz (20.8%). Output power also exhibits a broadband performance of 8.0±1.5 dBm from 220 to 295 GHz with power gain larger than 10.5 dB, corresponding to a large-signal 3-dB bandwidth larger than 75 GHz. This belongs to an excellent bandwidth in both small- and large-signal performance among the reported <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -band power amplifiers.

Определение потока и энергии активации десорбции фосфора при отжиге в потоке мышьяка подложки InP(001) в условиях молекулярно-лучевой эпитаксии

We report experimental study of phosphorus desorption from epi-ready InP(001) substrates during high-temperature annealing in an arsenic flux. InPAs solid solution and InAs islands form on the surface in the process of annealing. The original method is proposed for determining the number of phosphorus atoms desorbing from the surface by determining the number of arsenic atoms in the InPAs solid solution and InAs islands. The flux of phosphorus desorbing from the surface increases from 1 · 10−4 monolayer · cm−2· s−1 at 500◦C annealing temperature to 7.3 · 10−4 monolayer · cm−2· s−1 at 540◦C. The activation energy of the phosphorus desorption process is 2.7 ± 0.2 eV

Determination of the flow and activation energy of phosphorus desorption during annealing of an InP(001) substrate in an arsenic flux under molecular beam epitaxy conditions

We report experimental study of phosphorus desorption from epi-ready InP(001) substrates during high-temperature annealing in an arsenic flux. InPAs solid solution and InAs islands are formed on the surface in the process of annealing. The original method is proposed to determine the amount of phosphorus atoms desorbing from the surface by determining the amount of arsenic atoms in the solid solution of InPAs and InAs islands. The flux of phosphorus desorbing from the surface increases from 1·10-4 monolayer · cm-2·s-1 at 500oC annealing temperature to 7.3·10-4 monolayer · cm-2· s-1at 540oC. The activation energy of the phosphorus desorption process is 2.7±0.2 eV. Keywords: InP, annealing, desorption, activation energy.

A Study on the Consequence of Compressive and Tensile Strain on the Electronic Properties of InPNBi using Multi-band k dot p Hamiltonian

In order to find a potential and superior candidate for tandem solar cells, and Infra-Red (IR) photodetectors, we have thoroughly investigated the consequence of compressive and tensile strain on the electronic band diagram, and effective mass of InPNBi and compared the computed values for the lattice-matched condition with respect to the InP substrate using the 16-band k∙p perturbation Hamiltonian. We have anticipated that for a compressive strain of 0.98%, InP0.912N0.008Bi0.08 material system offers 1 eV bandgap, which can play a crucial role in designing efficient tandem solar cells. On the contrary, a bandgap of 0.776 eV and corresponding operating wavelength lying in the 1550 nm optical communication window can be achieved for InP0.91N0.08Bi0.01, which undergo a tensile strain of about 1.08% with respect to the host. Overall the bandgap reduction rate is largest in lattice-matched case, and higher in tensile strained compared to compressive strained InPNBi.

Investigation of the characteristics of the InGaAs/InAlGaAs superlattice for 1300 nm range vertical-cavity surface-emitting lasers

X-ray structural analysis and photoluminescence spectroscopy techniques were used to study heterostructures based on InGaAs/InAlGaAs superlattice for active regions of 1300 nm range lasers grown by molecular beam epitaxy. It is shown that the grown heterostructures have a high crystal quality. The perpendicular lattice mismatch of the average crystal lattice constant of the InGaAs/InAlGaAs superlattice with respect to the crystal lattice constant of the InP substrate is estimated at ~+0.01%. An analysis of the photoluminescence spectra made it possible to conclude that the contribution of Auger recombination is insignificant in the studied range of excitation power density. Studies of vertical-cavity surface-emitting lasers with an active region based on the InGaAs/InAlGaAs superlattice made it possible to estimate the gain coefficient at a level of 650 cm-1 for the standard logarithmic approximation of the dependence of the gain on the current density. The transparency current density of the laser was 400-630 A/cm2, which is comparable to the record low values for the case of highly strained InGaAs-GaAs and InGaAsN-GaAs quantum wells in the spectral ranges of 1300 nm, respectively. Keywords: superlattice, vertical-cavity surface-emitting laser, optical gain.

Reduction of optical transition energy in composite GaInAsBi quantum wells

Light emitting diode structures of quaternary GaInAsBi bismide quantum wells with AlInAs barriers were grown on InP substrates by molecular-beam epitaxy. Intermediate additional layers of GaInAs were inserted between the bismide quantum wells and AlInAs barriers to reduce the electron size-quantization energy and, therefore, the energy of optical transitions. It has been demonstrated both theoretically and experimentally that the redshift of emission wavelength in the composite GaInAs1−xBix (x∼0.06) quantum wells with the additional intermediate GaInAs layers can be as large as ∼0.4μm.

Towards Interband Cascade lasers on InP Substrate

In this study, we propose designs of an interband cascade laser (ICL) active region able to emit in the application-relevant mid infrared (MIR) spectral range and to be grown on an InP substrate. This is a long-sought solution as it promises a combination of ICL advantages with mature and cost-effective epitaxial technology of fabricating materials and devices with high structural and optical quality, when compared to standard approaches of growing ICLs on GaSb or InAs substrates. Therefore, we theoretically investigate a family of type II, “W”-shaped quantum wells made of InGaAs/InAs/GaAsSb with different barriers, for a range of compositions assuring the strain levels acceptable from the growth point of view. The calculated band structure within the 8-band k·p approximation showed that the inclusion of a thin InAs layer into such a type II system brings a useful additional tuning knob to tailor the electronic confined states, optical transitions’ energy and their intensity. Eventually, it allows achieving the emission wavelengths from below 3 to at least 4.6 μm, while still keeping reasonably high gain when compared to the state-of-the-art ICLs. We demonstrate a good tunability of both the emission wavelength and the optical transitions’ oscillator strength, which are competitive with other approaches in the MIR. This is an original solution which has not been demonstrated so far experimentally. Such InP-based interband cascade lasers are of crucial application importance, particularly for the optical gas sensing.

Systematic optical study of high-x InxGa1-xAs/InP structures for infrared photodetector applications

Optical and structural properties in high-x InxGa1-xAs (x > 0.65) samples with varying indium concentration grown on InP (100) substrate are reported. By increasing the indium fraction, it was found by the high-resolution X-ray diffraction (HR-XRD) study that the dislocation density in the InxGa1-xAs epitaxial layer significantly increased, and the surface quality deteriorated remarkably. Photoreflectance (PR) spectra show the presence of Franz-Keldysh Oscillations (FKOs) features above the InxGa1-xAs energy bandgap. The strain-induced electric field is then estimated directly from the FKOs periods. Temperature-dependent photoluminescence (TDPL) measurements from 10 K to 300 K showed carrier locations (S-shape). This abnormal behavior is due to the dislocation density associated with fluctuations in the indium concentration. A quasi-stationary rate equation model for the temperature-dependent luminescence spectra of the localized state material system is proposed to interpret the band gap emission process quantitatively. Low-temperature (10 K) time-resolved PL measurements show the increase of lifetime with increasing the indium concentration. Yet, the addition of only 1.7% of indium concentration results in a strong enhancement of PL lifetime by ∼ 80%.All these results reveal a more precise picture of the localization and recombination mechanisms of photogenerated carriers in the InGaAs layer, which could be the crucial factors in controlling the performance of high indium content InGaAs SWIR detector.

Evaluation of heat dissipation characteristics of quantum cascade laser with diamond submount using structure function and three-dimensional thermal fluid simulation

The heat dissipation of a quantum cascade laser (QCL) for a mounted structure with and without a diamond submount was evaluated by temperature and structure function measurements and three-dimensional simulation. From the structure function, it was shown that the thermal resistance between the QCL on the InP substrate and the CuW mount was reduced from 5.0 K W−1 without the submount to 2.5 K W−1 with the diamond submount. In the 3D simulation, it was confirmed that the heat flux transmitted horizontally through the diamond mount is larger than that without the submount. It is considered that the heat flux in the horizontal direction improved the heat dissipation from the InP substrate to the CuW mount. As a result, the output of the QCL with the submount was 1.15 times that of the QCL without the submount.

Influence of tin oxide (SnO2) interlayer on the electrical and reverse current conduction mechanism of Au/n-InP Schottky junction and its microstructural properties

The microstructural and current-voltage (I-V) characteristics of the prepared Au/SnO2/n-InP heterojunction (HJ) with an e-beam evaporated tin oxide (SnO2) film as an interlayer between the Au and InP substrate have been explored. The X-Ray diffraction and transmission electron microscopy results confirm the formation of the SnO2 thin film on InP surface. Then, the Au/SnO2/n-InP HJ diode is prepared and explored its electrical properties by the I-V approach. Low reverse leakage current is noted for HJ diode than the Au/n-InP Schottky junction (SJ). Higher barrier height (BH) is attained for the HJ compared to the SJ, which indicates that the insertion of SnO2 interlayer leads to an increase in the BH of SJ. Further, the BH is evaluated for the SJ and HJ diodes by Hernandez and Cheung's methods and matched with one another. Results exhibit that the interface state density (NSS) of HJ is less than the SJ, suggesting that the use of the SnO2 layer plays a key role in reducing NSS. Analysis of the reverse leakage current transport suggested the dominance of Poole-Frenkel emission in the lower bias region while the Schottky emission mechanism governs at upper bias region in both the SJ and HJ diodes. These results could provide expedient information of SnO2 interlayer for the design of metal/interlayer/semiconductor or heterojunction devices.