III-V Compound Research Articles

Atomic Layer Deposition of Multi-Component Films Using Precursor Co-Dosing

A growing number of ALD applications require the deposition of ternary or quarternary compounds. Examples include doped films (e.g. ZnO:Al), mixed oxides to tune dielectric properties (e.g. HfZrO), tunable bandgap materials for solar cells (e.g. ZnOS) or opto-electronic materials (e.g. InGaN), and high mobility oxide semiconductors (e.g. InGaZnO). A common method to deposit multicomponent films in ALD is the supercycle approach [1], where sub-cycles of different binary compounds are combined to deposit films where the resulting net composition is determined by the cycle ratio of the individual sub-cycles. A drawback of the supercycle method is that essentially multilayer stacks are deposited instead of true alloys and the film composition varies out-of-plane, potentially impacting film properties.An alternative method is to use precursor co-dosing, where two or more precursors are simultaneously dosed and co-adsorb during a half-reaction. The resulting film composition is then determined by the ratio of the partial pressures of the individual precursors during the precursor dose. As each ALD cycle deposits a true alloy, it results in excellent out-of-plane compositional uniformity. The co-dosing method has first been reported in the late 1980’s to deposit ternary and quarternary III-V compounds [2] and has been used since for a wide range of materials. In the last decade it has become the method of choice for depositing multicomponent materials with Spatial ALD.A proper understanding of the relation between film composition and precursor partial pressure during co-dosing is essential for accurate control of the film composition. This is not straightforward, as the surface chemistry of co-dosing can be quite complex, involving competitive adsorption, heterogeneity of reactive sites, exchange reactions and more. We will discuss how the surface chemistry of precursor co-dosing determines the film composition. In analogy to the IUPAC classification of adsorption isotherms for single adsorbents [3], we will introduce a similar classification of adsorption isotherms for multiple absorbing precursors which we will use to review and explain results reported in literature. Finally, we will discuss some interesting new opportunities for co-dosing, such as the deposition of gradient composition films and the use of co-dosing for area-selective deposition.[1]: A. Mackus et al, Chem. Mater. 31 (2019) 1142[2]: M. Tischler, S. Bedair, J. Cryst. Growth 77 (1986) 89[3]: M. Thommes et al, Pure & Appl. Chem. 87 (2015) 87

Morphological and Electrical Characterization of AlGaN/GaN Heterostructures Modified By Atomic Layer Etching

Modern microelectronic components for high-power and high-frequency applications based on III-V compound semiconductors offer high break down voltage (GaN: 5 MV/cm and AlN: 15 MV/cm) at low specific on-resistance. However, it requires reliability and reproducibility of the production processes. Going to higher frequencies (5 GHz and beyond) and more integration in consumer electronics, smaller structure sizes are needed. This is going along with increasing demands on the manufacturing processes like dry etching. The main goal is to reach smaller and high controllable etching rates, going down to single atomic layers, low damage, and minimized surface roughness. Atomic layer etching (ALE) represents a key technology in order to achieve such requirements.An ALE process consists of two independent steps forming a repeatable cycle with a specific etching amount per cycle (EPC). First a surface modification is done by a chemical precursor i.e., adsorbing or oxidizing the surface. The second step is the removal of the modified layer, either physically by low energy non-reactive ion bombardment (Plasma Enhanced ALE [PEALE]) or chemically by a reactive species (Thermal ALE). The two steps are separated by an inert gas purge. This purging grants the removal of the chemistry after the first step, preventing further chemical reaction and transporting the chemical products out of the chamber after the second step.In this study, a PEALE conducted on different tools is used, for gate and contact recess study in a AlGaN/GaN heterostructure to form high electron mobility transistors (HEMT) with reduced ohmic contact resistance and threshold voltages. The results show a reduction of ohmic contact resistance at reduced forming temperatures and a linear dependence of the threshold voltage on gate recess depth. In order to determine the etching rate and roughness, atomic force microscopy (AFM) measurements were performed.The PEALE module is either integrated into a cluster tool consisting of atomic layer deposition (ALD) and chemical vapor deposition (CVD) or done in a combined ALD/ALE chamber. This opens the possibility of etching and depositing in-situ, reducing contamination and degradation of the substrate material.By this means, metal insulator semiconductor (MIS)-HEMTS with a recessed gate are studied. The monitoring of the individual processes is achieved by test structures like transfer length method structures (TLM) and metal oxide semiconductor (MOS), which showed the improved electric performance of these devices and may indicate unwanted interface issues, respectively. Additional, pre- and post-treatments could improve the interfaces further. The results will be presented and discussed in terms of ALE process development and optimization.This work was financially supported within the ALEStar project by the government of the Free-state of Saxony and the European Regional Development Fund under grant no. SAB 100402929.

Recent Research on Indium-Gallium-Nitride-Based Light-Emitting Diodes: Growth Conditions and External Quantum Efficiency

The optimization of the synthesis of III-V compounds is a crucial subject in enhancing the external quantum efficiency of blue LEDs, laser diodes, quantum-dot solar cells, and other devices. There are several challenges in growing high-quality InGaN materials, including the lattice mismatch between GaN and InGaN causing stress and piezoelectric polarization, the relatively high vapor pressure of InN compared to GaN, and the low level of incorporation of indium in InGaN materials. Furthermore, carrier delocalization, Shockley–Read–Hall recombination, auger recombination, and electron leakage in InGaN light-emitting diodes (LEDs) are the main contributors to efficiency droop. The synthesis of high-quality III-V compounds can be achieved by optimizing growth parameters such as temperature, V/III ratios, growth rate, and pressure. By reducing the ammonia flow from 200 sccm to 50 sccm, increasing the growth rate from 0.1 to 1 m/h, and lowering the growth pressure from 250 to 150 Torr, the external quantum efficiency of III-V compounds can be improved at growth temperatures ranging from 800 °C to 500 °C. It is crucial to optimize the growth conditions to achieve high-quality materials. In addition, novel approaches such as adopting a microrod crystal structure, utilizing the piezo-phototronic effect, and depositing AlN/Al2O3 on top of the P-GaN and the electron-blocking layer can also contribute to improving the external quantum efficiency. The deposition of a multifunctional ultrathin layers of AlN/Al2O3 on top of the P-GaN can enhance the peak external quantum efficiency of InGaN blue LEDs by 29%, while the piezo-phototronic effect induced by a tensile strain of 2.04% results in a 183% increase in the relative electroluminescence intensity of the LEDs. This paper also discusses conventional and inverted p-i-n junction structures of LEDs.

Two-dimensional semiconductors based field-effect transistors: review of major milestones and challenges

Two-dimensional (2-D) semiconductors are emerging as strong contenders for the future of Angstrom technology nodes. Their potential lies in enhanced device scaling and energy-efficient switching compared to traditional bulk semiconductors like Si, Ge, and III-V compounds. These materials offer significant advantages, particularly in ultra-thin devices with atomic scale thicknesses. Their unique structures enable the creation of one-dimensional nanoribbons and vertical and lateral heterostructures. This versatility in design, coupled with their distinctive properties, paves the way for efficient energy switching in electronic devices. Moreover, 2-D semiconductors offer opportunities for integrating metallic nanoribbons, carbon nanotubes (CNT), and graphene with their 2-D channel materials. This integration helps overcome lithography limitations for gate patterning, allowing the realization of ultra-short gate dimensions. Considering these factors, the potential of 2-D semiconductors in electronics is vast. This concise review focuses on the latest advancements and engineering strategies in 2-D logic devices.

Achievement of extremely small subthreshold swing in Vertical Source-All-Around-TFET with suppressed ambipolar conduction

In this manuscript, we come up with a new line-tunneling-based channel-engineered GaAsSb/GaSb heterojunction Source-All-Around Vertical Nanowire TFET (SAA-NW-VTFET) and analyzed by Sentaurus TCAD-3D simulation. In this proposed model, increased tunneling area at the source-channel interface and the n+-pocket region, along with selective III-V compound semiconductors, have boosted the ON-current in the device. On the other hand, non-uniform channel doping and reduced tunneling area at the drain end have significantly suppressed the ambipolar current. The significant results in terms of ON-current (ION = 0.789 × 10−4 A/μm), OFF-current (IOFF = 1.08 × 10−17 A/μm), ION/IOFF ratio (7.25 × 1012), threshold voltage (0.2 V), point subthreshold swing (SS = 3 mV/dec) and average SS (SSavg = 7 mV/dec) are obtained in the simulation study. In addition, the effect of temperature (250 K–450 K) on device DC characteristics and DIBT is also presented.

Thermal strain relaxation of GaAs overgrown on nanovoid based Ge/Si substrate

The integration of high quality III-V materials-based devices on the Si platform is considered as an enabling path towards achieving the long-standing goal of creating low-cost/high-performance devices. However, the heteroepitaxy of III-V compounds on a Si substrate generates high stress due to the difference in thermal expansion coefficient leading notably to crack generation. Here, we report on the reduction of the thermal strain of GaAs and Ge deposited on a Si substrate. The method is based on the formation of buried high density nanovoids by electrochemical etching of Ge/Si virtual substrate followed by direct epitaxial growth of Ge and GaAs. The thermal strain has been investigated for GaAs epilayer by High-Resolution X-Ray Diffraction and Raman spectroscopy showing a 30% decrease in strain. The strain reduction relies on the nanovoids-mediated thermal strain accommodation. Furthermore, photoluminescence measurements showed a 10-fold increase of the intensity, resulting in an improved optical and crystalline quality, making this virtual substrate promising for III-V based devices on Silicon.

Analysis of Temperature-Dependent Photoluminescence Spectra in Mid-Wavelength Infrared InAs/InAsSb Type-II Superlattice

Photoluminescence (PL) is one of the commonly used methods to determine the energy gap ({E}_{mathrm{g}}) of semiconductors. In order to use it correctly, however, the shape of the PL peak must be properly analyzed; otherwise, the value of {E}_{mathrm{g}} is burdened with a large error. {E}_{mathrm{g}} is often mistakenly attributed to the PL peak position, which in type-II superlattices (T2SLs) exhibits typical “S-shaped” behavior as a function of temperature, significantly different from the Varshni model used to define the energy gap of III-V compounds. The position peak of the PL relative to the real {E}_{mathrm{g}} in T2SLs is red-shifted because of the carrier localization at low temperatures and blue-shifted because of the free carrier emission at high temperatures. To correctly determine {E}_{mathrm{g}}, the shape of the PL peak should be analyzed using the theoretical PL line shape model that takes into account both localized (below the bandgap) and free carriers (above the bandgap) emissions. This work shows that the use of such a model to analyze the shape of the PL signal gives the correct results of determining {E}_{mathrm{g}} for mid-wave infrared InAs/InAsSb T2SL, which showed a significant contribution of localized states in optical transitions and characteristic “S-shaped” PL peak behavior. This allowed us to determine the correct values of the Varshni coefficients for a given T2SL. The result also agrees with the theoretical calculations of {E}_{mathrm{g}} made using the k·p method.

Competitive Relaxation Mechanisms in Strained Epitaxial InGaSb on GaSb Substrate

Hetoroepitaxial growth of III-V compounds can produce both novel structures for fundamental research and electronic/photonic devices for practical applications. Antimony-based compounds are interested since they can interact with light in longer wavelengths ranging from near-infrared to terahertz frequency domains. In this work, we present an experimental observation of step-decorated surface and dislocation lines formed in an epitaxial In0.17Ga0.83Sb layer. The growth is performed by solid-source molecular beam epitaxy on (001) GaSb substrate at 400°C with the InGaSb deposition rate of 0.12 monolayer per second. The atomic force microscopy shows that the regular atomic steps are generally misaligned with the surface dislocation lines. The average distance between the steps is about 200 nm and the presence of dislocation lines affects the subsequent growth. Zigzag step-edge structure observed near the intersection of the step-edges and the dislocation lines can be explained by simple strain-considered models. Enhanced and depleted growth areas can be related to the degree of underneath strain. The understanding of this phenomena might lead to the simple and practical realization of regular arrays of nanostructures such as quantum wires and quantum dots.

(Invited) Enhanced Photocatalysis on TiO2-Passivated III-V Compound Semiconductors and 2D Material Heterostructures for Water Splitting and CO2 Reduction

We report enhanced photocatalysis for H2 evolution and CO2 reduction using TiO2-passivated InP and GaAs photocathodes.1-4 The TiO2 layer makes the InP semiconductor photochemically stable. This represents a major step forward in photocatalysis, which has typically been limited to metal oxide materials. In addition to making these surfaces stable, the TiO2 film, deposited by atomic layer deposition (ALD), also provides a substantial enhancement in the efficiency of H2 evolution. We find that passivating GaAs with just a few nm of TiO2 produces a shift in the onset potential of H2 evolution by +0.35 V at 1 mA/cm2 and enhances the photocurrent by 32-fold over bare GaAs (at 0 V vs. RHE). Here, thinner TiO2 films produce a larger enhancement than thicker films, which correlates with the higher density of O-vacancies (i.e., Ti3+ surface states) observed in these thinner films using X-ray photoemission spectroscopy (XPS). While TiO2 films 1-5nm thick produce large enhancements, no enhancement is observed for TiO2 thicknesses above 10 nm, which are crystalline and, therefore, considerably more insulating than thinner amorphous TiO2 films.Using transient reflectance spectroscopy (TRS), we measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interfaces in situ under various electrochemical potentials.5 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes.We also demonstrated plasmon-resonant enhancement of photocatalysis on monolayer WSe2.6 In addition, we measured the stacking dependence and resonant interlayer excitation of monolayer WSe2/MoSe2 heterostructures for photocatalytic energy conversion.7 Qiu, J., G. Zeng, M. Ge, S. Arab, M. Mecklenburg, B. Hou, C. Shen, A.V. Benderskii and S.B. Cronin, Correlation of Ti3+ states with photocatalytic enhancement in TiO2-passivated p-GaAs. Journal of Catalysis, 337, 133 (2016).Qiu, J., G.T. Zeng, M.A. Ha, M.Y. Ge, Y.J. Lin, M. Hettick, B.Y. Hou, A.N. Alexandrova, A. Javey and S.B. Cronin, Artificial Photosynthesis on TiO2-Passivated InP Nanopillars. Nano Letters, 15, 6177-6181 (2015).Qiu, J., G.T. Zeng, M.A. Ha, B.Y. Hou, M. Mecklenburg, H.T. Shi, A.N. Alexandrova and S.B. Cronin, Microscopic Study of Atomic Layer Deposition of TiO2 on GaAs and Its Photocatalytic Application. Chemistry of Materials, 27, 7977-7981 (2015).Wang, Y. and S.B. Cronin, Performance Enhancement of TiO2-encapsulated Photoelectrodes Based on III–V Compound Semiconductors, in Ultrathin Oxide Layers for Solar and Electrocatalytic Systems. 2022, Royal Society of Chemistry. p. 103-134.Xu, Z.H., B.Y. Hou, F.Y. Zhao, Z. Cai, H.T. Shi, Y.W. Liu, C.L. Hill, D.G. Musaev, M. Mecklenburg, S.B. Cronin and T.Q. Lian, Nanoscale TiO2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Letters, 21, 8017-8024 (2021).Chen, J., C.S. Bailey, Y. Hong, L. Wang, Z. Cai, L. Shen, B. Hou, Y. Wang, H. Shi, J. Sambur, W. Ren, E. Pop, and S.B. Cronin., Plasmon-Resonant Enhancement of Photocatalysis on Monolayer WSe2. ACS Photonics, 6, 787 (2019).Chen, J., C.S. Bailey, D. Cui, Y. Wang, B. Wang, H. Shi, Z. Cai, E. Pop, C. Zhou and S.B. Cronin, Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).

Ⅲ-V Compound Semiconductor Multijunction Solar Cells and their Low-Cost Manufacturing Technique

Ⅲ-V Compound Semiconductor Multijunction Solar Cells and their Low-Cost Manufacturing Technique

Preparation and Investigation of Micro-Transfer-Printable Single-Crystalline InP Coupons for Heterogeneous Integration of III-V on Si

New requirements for high-frequency applications in wireless communication and sensor technologies need III-V compound semiconductors such as indium phosphide (InP) to complement silicon (Si)-based technologies. This study establishes the basis for a new approach to heterogeneous integration of III-V on Si aimed at the transfer of single-crystalline InP coupons on Si via micro-transfer printing (μTP). The InP coupons will act as high-quality virtual substrates that allow selective homo-epitaxy. We present the chemical-mechanical polishing-based preparation and structural characterization of µm-thin (001) InP platelets, starting from high-quality 4-inch bulk crystals and micro-patterning into transferable coupons of several hundred µm2. The obtained InP platelets exhibit the desired thickness—below 10 ± 1 µm—and low surface roughness—<0.3 nm—on both sides, meeting the precondition for µTP and epitaxy. X-ray rocking curve measurements provide accurate spatial maps of the total strain, which indicate small strain variations in the µm-thin InP sample. Rocking curve mappings of the (0 0 4) reflection reveal half-widths below 16 arcsec in the majority of the sample area after thinning that is similar to commercially available InP bulk substrates. Pole figure measurements show no evidence of stress-induced micro-twinning or stacking faults. Overall, minor indications of crystal quality degradation in the product platelets, compared with the bulk samples, were detected.

Direct bonding of LiNbO3 and GaAs at room temperature by using activated Si atom layer

Heterogeneous integration of LiNbO3 and GaAs at room temperature has been achieved by using an activated Si atom interlayer, which demonstrate effectiveness in the fabrication of GaAs based LiNbO3 wafer. By using the activated Si atom interlayer as the adhesive layer, 4-inch LiNbO3 wafer is successfully directly bonded to the surface of GaAs wafer. The wafer bonding rate reaches over 95%. After bonding, the LiNbO3/GaAs bonding pair is cut into 10 × 10 mm2 square bonded chips. After annealing, the maximum bonding strength of square bonded chips exceeds 22 MPa. This means that the bonding strength of LiNbO3/GaAs wafer can be comparable to that of bulk materials. The characterization results of the bonding interface confirm that the intermediate amorphous Si layer is effective in improving the bonding strength and quality of LiNbO3/GaAs heterojunction. Heterogeneous integration of LiNbO3 with GaAs and other Ⅲ-Ⅴ compound semiconductor materials is conducive to reducing the area occupied by optical communication platforms and improving the overall efficiency of devices.

Sb-Based Low-Noise Avalanche Photodiodes

Accurate detection of weak optical signals is a key function for a wide range of applications. A key performance parameter is the receiver signal-to-noise ratio, which depends on the noise of the photodetector and the following electrical circuitry. The circuit noise is typically larger than the noise of photodetectors that do not have internal gain. As a result, a detector that provides signal gain can achieve higher sensitivity. This is accomplished by increasing the photodetector gain until the noise associated with the gain mechanism is comparable to that of the output electrical circuit. For avalanche photodiodes (APDs), the noise that arises from the gain mechanism, impact ionization, increases with gain and depends on the material from which the APD is fabricated. Si APDs have established the state-of-the-art for low-noise gain for the past five decades. Recently, APDs fabricated from two Sb-based III-V compound quaternary materials, AlxIn1-xAsySb1-y and AlxGa1-xAsySb1-y, have achieved noise characteristics comparable to those of Si APDs with the added benefit that they can operate in the short-wave infrared (SWIR) and extended SWIR spectral regions. This paper describes the materials and device characteristics of these APDs and their performance in different spectral regions.

Considerations for excess noise measurements of low-k-factor Sb-based avalanche photodiodes.

In applications where high sensitivity is required, the internal gain mechanism of avalanche photodiodes can provide a performance advantage relative to p-i-n photodiodes. However, this internal gain mechanism leads to an excess noise that scales with gain. This excess noise term can be minimized by using materials systems in which impact ionization is initiated primarily by one carrier type. Recently, two Sb-based materials systems, AlInAsSb and AlGaAsSb, have exhibited exceptionally low excess noise, particularly for III-V compound materials. There are four important considerations that can impact the excess noise measurements in such low-noise materials. These considerations deal with the excess noise factor calculation method, measurement RF frequency, measurement wavelength, and the gain calculation method. In this paper, each of these factors is discussed, and their implications on excess noise are considered.

GaAs hetero-epitaxial layers grown by MOVPE on exactly-oriented and off-cut (1 1 1)Si: Lattice tilt, mosaicity and defects content

Integration of III-V devices with Si-photonics and fabrication of monolithic III-V/Si tandem solar cells require the heteroepitaxy of III-V compounds on Si. We report on the lattice tilt, mosaicity and defects content of relaxed GaAs grown by MOVPE on exactly-oriented and 4°-offcut (111)Si. Thin GaAs single-layers grown at 400 °C and annealed at 700 °C show ∼ 3 × 108 cm−2 density of surface pinholes. Double-layer samples were obtained by GaAs overgrowth at 700 °C. GaAs epilayers are tilted by (0.05–0.14)° with respect to Si. Rotational twins were observed in X-ray diffraction (XRD) pole figures: the most abundant ones originate from 60°-rotation of GaAs around the 1¯1¯1¯ growth direction and are identified as micro-twins along the GaAs/Si hetero-interface. Twins obtained by rotations around the 1¯1¯1, 11¯1¯, and 1¯11¯ directions or by combined rotations around the growth direction and one of the former, were also observed. The GaAs mosaicity and block size were studied through high-resolution XRD intensity mapping: for single-layer samples crystal blocks are ascribed to 3–5 nm thin micro-twins, whose size does not change upon annealing. In double-layer samples thicker (32–35 nm) micro-twins occur. GaAs samples grown on offcut (111)Si show less rotational twins but a reduced mosaic block size with respect to exactly-oriented Si.

Application of TiO2/Ag/TiO2 as an Ohmic Contact to an AlGaAs Layer in a GaAs Solar Cell

This paper investigates the possibility of using a nanolaminate TiO2/Ag/TiO2 structure as a transparent conductive coating on GaAs solar cells. A novel result is that this structure forms an Ohmic contact to Al-rich AlGaAs, which is used as a “window” layer in GaAs-based solar cells. The TiO2/Ag/TiO2 structure is deposited by RF magnetron sputtering at room temperature. This nanolaminate coating has good optical and electrical properties: a high transmittance of 94% at 550 nm, a sheet resistance of 7 Ω/sq, and a figure of merit (FOM) of 105 × 10−3 Ω−1. These properties are the result of the presence of a discontinuous layer of Ag between two thin layers of TiO2. The morphology of a discontinuous layer of Ag nanogranules is confirmed by the observation of a cross-section of a sample with high-resolution transmission electron microscopy (HRTEM) and EDX analyses. Current–voltage diode characteristics of GaAs solar cells measured under standard test illumination at 1000 W/m2 are analyzed. The formation of an Ohmic contact is explained by the Fermi-level pinning effect caused by nanosized Ag particles in the nanolaminate TiO2/Ag/TiO2 structure. The obtained results demonstrate a new application of oxide−metal−oxide (OMO) coatings as Ohmic contacts to III-V compound semiconductors.

Analysis for Expansion of Driving Distance and CO2 Emission Reduction of Photovoltaic-Powered Vehicles

Development of photovoltaic (PV)-powered vehicles is very important to play a critical role in a future carbon neutrality society because it has been reported that the vehicle integrated PVs (VIPVs) have great ability to reduce CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emission from the transport sector. Usage of high-efficiency solar cell modules is essential due to the limited installable area of PV on vehicle exterior. This article presents test driving data of the Toyota Prius demonstration car installed with high-efficiency III-V compound triple-junction solar cell module with an efficiency of more than 30%. Average daily driving distance (DD) of 17 km/day under usage of air conditioning and 62% CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emission reduction are demonstrated by actual driving in Nagoya, Japan. In addition, analytical results for impact of high-efficiency VIPV modules of more than 35% on increases in DD of more than 30 km/day average and reducing CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emission of PV-powered vehicles of more than 70% reduction are also shown.

Enhanced thermoelectric performance of InSb through deep level impurity donor state induced by La doping

As one member of III-V semiconductors that have a variety of applications, InSb also shows great potential in thermoelectrics owing to its high mobility. In this work, the thermoelectric performance of n-type polycrystalline InSb is improved by La doping, which induces deep level impurity donor state and massive defects, synergistically optimizing both electrical and thermal transport properties. The peak power factor of La-doped InSb is enhanced from 42 to 58 μW cm−1 K−2 at 773 K due to the enlarged carrier concentration provided by the deep level donor state. Meanwhile, lattice thermal conductivity decreases from 3.2 to 1.7 W m−1 K−1 at 773 K due to In precipitates, point defects and local atomic disorder. Consequently, the peak zT of La-doped InSb is promoted to 0.85 at 773 K, which is among the best value in III-V compounds.

Sb-Mediated Tuning of Growth- and Exciton Dynamics in Entirely Catalyst-Free GaAsSb Nanowires.

Vapor-liquid-solid (VLS) growth is the mainstream method in realizing advanced semiconductor nanowires (NWs), as widely applied to many III-V compounds. It is exclusively explored also for antimony (Sb) compounds, such as the relevant GaAsSb-based NW materials, although morphological inhomogeneities, phase segregation, and limitations in the supersaturation due to Sb strongly inhibit their growth dynamics. Fundamental advances are now reported here via entirely catalyst-free GaAsSb NWs, where particularly the Sb-mediated effects on the NW growth dynamics and physical properties are investigated in this novel growth regime. Remarkably, depending on GaAsSb composition and nature of the growth surface, both surfactant and anti-surfactant action is found, as seen by transitions between growth acceleration and deceleration characteristics. For threshold Sb-contents up to 3-4%, adatom diffusion lengths are increased ≈sevenfold compared to Sb-free GaAs NWs, evidencing the significant surfactant effect. Furthermore, microstructural analysis reveals unique Sb-mediated transitions in compositional structure, as well as substantial reduction in twin defect density, ≈tenfold over only small compositional range (1.5-6% Sb), exhibiting much larger dynamics as found in VLS-type GaAsSb NWs. The effect of such extended twin-free domains is corroborated by ≈threefold increases in exciton lifetime (≈4.5ns) due to enlarged electron-hole pair separation in these phase-pure NWs.

InSb-based saturable absorbers for ultrafast photonic applications.

Sb-related III-V compounds have recently gained great research interest owing to their excellent optical and electrical characteristics, which provide many possibilities in photonics and electronics. This study investigated the application of InSb films in ultrafast photonics. An InSb film was fabricated on the tapered zone of a microfiber, and its saturation intensity, modulation depth, and non-saturable loss were determined as 119.8 MW cm-2, 23.5%, and 27.3%, respectively. The structure of the electronic band and density of states of InSb were theoretically calculated. Notably, mode-locked and Q-switched fiber lasers were realised by incorporating the InSb-microfiber device into two different Er-doped fiber cavities. In the Q-switching state, the narrowest pulse duration was measured as 1.756 μs with a maximum single-pulse energy of 221.95 nJ and a signal-to-noise ratio of 60 dB. In the mode-locking operation, ultrafast lasers with a high signal-to-noise ratio (70 dB), a pulse width as narrow as 265 fs and a repetition rate of 49.51 MHz were acquired. Besides, the second-harmonic mode-locked state was built with an output power of 13.22 mW. In comparison with the reported laser performance with 2D materials as saturable absorbers, the InSb-based mode-locked and Q-switched fiber lasers proposed herein exhibit better comprehensive performance.