Semi-insulating InP Substrate Research Articles

InGaAs/AlInAsSb avalanche photodiodes with low noise and strong temperature stability

High-sensitivity avalanche photodiodes (APDs) are used to amplify weak optical signals in a wide range of applications, including telecommunications, data centers, spectroscopy, imaging, light detection and ranging, medical diagnostics, and quantum applications. This paper reports antimony-based separate absorption, charge, and multiplication structure APDs on InP substrates. Al0.7In0.3As0.79Sb0.21 is used for the multiplier region, and InGaAs is used as the absorber. The excess noise is comparable to that of silicon APDs; the k-value is more than one order of magnitude lower than that of APDs that use InP or InAlAs for the gain region. The external quantum efficiency without an anti-reflection coating at 1550 nm is 57%. The gradient of the temperature coefficient of avalanche breakdown voltage is 6.7 mV/K/μm, which is less than one-sixth that of InP APDs, presenting the potential to reduce the cost and complexity of receiver circuits. Semi-insulating InP substrates make high-speed operation practical for widely reported AlxIn1−xAsySb1−y-based APDs.

InGaAs-based Gunn light emitting diode

We report an n-type In0.53Ga0.47As based Gunn light emitting diode operated at around 1.6 μm. The device structure comprises of an n-type In0.53Ga0.47As epilayer with a thickness of 5 μm grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on a semi-insulating InP substrate and fabricated in a planar architecture with a stepped structure at anode side to suppress the destructive effect of high built-in electric field in propagating Gunn domain. Gunn diode is operated under pulsed voltage with a pulse width of 60 ns and pulse duration of 4.5 ns to keep the duty cycle as low as 0.0013%. The Gunn oscillations with an 1 ns period are observed at around 4.1 kV/cm, which corresponds to the electric field threshold of Negative Differential Resistance (NDR). The light emission at around 1.6 μm also starts at the threshold electric field of the NDR region (E = 4.2 kV/cm) of the current-voltage curve, and the emission intensity increases drastically with increasing applied electric field. The observed light emission at NDR threshold electric field where Gunn oscillations appear on the voltage pulse is attributed to the impact ionisation process occurring in the current domains along the sample, which generates excess carriers to initiate the band-to-band recombination in In0.53Ga0.47As.

Electrical Activity of Extended Defects in Relaxed InxGa1−xAs Hetero-Epitaxial Layers

The electrical activity of extended defects in III–V materials, combining different analysis methods based on lifetime extraction from diode current-voltage characteristics, time resolved photoluminescence (TRPL) and deep level studies using Deep Level Transient Spectroscopy (DLTS) is reviewed. To that purpose p+n junction diodes have been fabricated in In0.53Ga0.47As hetero-epitaxial layers on semi-insulating InP or GaAs substrates. By depositing a strained buffer layer, the Extended Defect Density (EDD) can be varied over several decades, enabling a systematic study of their electrical impact in the same range. The defect densities are determined by High-Resolution X-ray Diffraction (HR-XRD), DLTS and Electron Channeling Contrast (ECCI) techniques. The generation and recombination (GR) lifetimes of the In0.53Ga0.47As layers become dominated by the EDs for densities above about 3 × 107 cm−2, whereby the dominant GR level moves closer to the mid gap position. This is supported by DLTS investigations, showing the occurrence of specific electron traps for defective epi layers, which exhibit a capture behavior that is typical for extended defects.

Криогенные термометры сопротивления на основе пленок Ge–InP. Технология и конструирование в электронной аппаратуре

Despite the large number of scientific articles devoted to the development of cryogenic resistance thermometers, not many of these thermometers are mass-produced. As is know, semiconductor resistive temperature sensors have low magnetoresistance and high resistance to radiation. The purpose of this work was to manufacture thin (170—190 nm) Ge films on semi-insulating InP substrates, which can be used to create cryogenic resistance thermometers with high temperature sensitivity and relatively low sensitivity to magnetic field that can operate in the 1.5—400 К temperature range. Films of Ge on InP (100) can be used to produce cryogenic resistance thermometers. They have good thermal sensitivity and relatively low magnetoresistance. The films were produced by thermal evaporation of Ge in vacuum (2•10-4 Pa) on semi-insulating InP (100) substrates. The temperature of the InP substrate during film deposition was 310°C, the deposition rate was also constant during sputtering, but varied in the range of 0.03 to 0.06 nm/s for different films. Ge films were p-type conductivity with a resistivity of 0.2—0.3 Ω•cm, hole concentration (3—5)•1018 cm–3 and Hall mobility 6.5—7.5 сm2/(V•s) at room temperature. The quality of the Ge–InP heterostructure was determined by high-resolution X-ray diffraction on a Philips MRD diffractometer. The nanomorphology of the surface of Ge films was studied using the NanoScope IIIa atomic force microscope. The crystal structure of the films is amorphous or polycrystalline with a low level of structural perfection. The effective value of the surface roughness is from 2.25 to 2.60 nm. The obtained resistance values at different temperature in the range of 2—25 K were described by exponential dependence. Corrections in temperature measurement are 5% in a magnetic field of 11 T at a temperature of 4.2 K and 14% in a magnetic field of 14 T at a temperature of 2.2 K. The research results indicate that the obtained films can be used to measure cryogenic temperatures in magnetic fields of up to 14 T.

The impact of extended defects on the generation and recombination lifetime in n type In.53Ga.47As

The relationship between the threading dislocation density (TDD), the generation (τg) and recombination lifetime (τr) in relaxed n-type In.53Ga.47As is investigated for a series of p+n junction diodes, containing a TDD ranging from 105 to 1010 cm−2. The TDs are generated intentionally by lattice-misfit growth on semi-insulating (SI) InP and GaAs substrates. The lifetimes have been extracted from diode current–voltage (I–V) and photoluminescence (PL) analysis showing that TDDs affect their values above a density of about 1 × 107 cm−2 (τg,E ~ 0) and about 1 × 108 cm−2 (τr and τPL), which can be well-explained by the charged dislocation cylinder model. In addition, a detailed comparison between the results from deep level transient spectroscopy and from the diode characterization is performed, showing that the responsible G/R center shifts toward mid-gap in In.53Ga.47As and transfers from a native point defect (PD1) to a TD (E2/H1). Finally, the classical concept of generation lifetime and recombination lifetime in terms of dislocations is discussed based on the results.

(Invited) Electrical Activity of Extended Defects in III-V Semiconductors

This paper gives an overview on the electrical activity of extended defects in III-V materials, combining different analysis methods, which are based on lifetime extraction from diode current-voltage characteristics and deep-level studies using Deep-Level Transient Spectroscopy (DLTS). To that purpose p+n junction diodes have been fabricated in In0.53Ga0.47As hetero-epitaxial layers on semi-insulating InP or GaAs substrates. By depositing a strained buffer layer, the Extended Defect Density (EDD) can be varied over several decades, enabling the study of the electrical impact in the same range. It will be shown that the generation and recombination (GR) lifetimes of the In0.53Ga0.47As layers become dominated by the EDs for densities above about 3×106 cm-2, whereby the dominant GR level moves closer to the mid gap position. This is supported by DLTS, showing the occurrence of specific electron traps for defective epi layers, which exhibit a capture behavior which is typical for extended defects.

Hybrid epitaxy technique for the growth of high-quality AlInAs and GaInAs layers on InP substrates

The quality and properties of epitaxial films are strongly determined by the reactor type and the precursor source phase. Such parameters can impose limitations in terms of background doping, interface sharpness, clustering, phase separation, and homogeneity. The authors have implemented a hybrid epitaxy technique that employs, simultaneously, vapor and solid sources as group III precursors. The system combines the high throughput and the versatility of gas sources as well as the high purity of solid sources. Using this technique, the authors successfully demonstrated epitaxial growth of Al0.48In0.52As and Ga0.47In0.53As layers on Fe-doped semi-insulating InP (001) substrates with interesting properties, compared with the epilayers grown by more standard techniques (chemical beam epitaxy, metal-organic chemical vapor deposition, and MBE). For AlInAs growth, trimethylindium and solid aluminum were used as In and Al precursors, respectively. In the case of GaInAs, triethylgallium and solid indium were used, respectively, as Ga and In precursors. Thermally cracked arsine (AsH3) was used as an As (group V) precursor for both alloys. The AlInAs and GaInAs epilayers grown at a temperature of 500 °C exhibited featureless surfaces with RMS roughness of 0.2 and 1 nm, respectively. Lattice mismatch is of 134 ppm, for AlInAs, and −96 ppm, for GaInAs, which were determined from high-resolution x-ray diffraction (HR-XRD) patterns and showed a large number of Pendellösung fringes, indicating a high crystalline quality. An FWHM of 18.5 arcs was obtained for GaInAs epilayers, while HR-XRD mapping of a full 2-in. wafer confirmed a viable lattice mismatch homogeneity (standard deviation of 0.026%) for as-grown layers. The authors observed room-temperature background doping values as low as 3 × 1015 cm−3, for AlInAs, and 1 × 1015 cm−3, for GaInAs. Analysis of the PL spectra at 20 K showed an FWHM of 8 meV, for AlInAs, and 9.7 meV, for GaInAs, demonstrating a very good optical quality of the epilayers. In addition, they have investigated the effects of the growth temperature and of the arsine pressure on epilayer properties. They also discuss the optimum conditions for the growth of high-quality Al0.48In0.52As and Ga0.47In0.53As layers on InP (001) substrates using this hybrid epitaxy technique.

InGaAs Diodes for Terahertz Sensing-Effect of Molecular Beam Epitaxy Growth Conditions.

InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for development of compact THz imaging systems. To further optimize design for sensitive and broadband THz detection, one of the major challenges remains: to understand the noise origin, influence of growth conditions and role of defects for device operation. We present a detailed study of photoreflectance, low-frequency noise characteristics and THz sensitivity of InGaAs bow-tie diodes. The diodes are fabricated from InGaAs wafers grown by molecular beam epitaxy (MBE) on semi-insulating InP substrate under different technological conditions. Photoreflectance spectra indicated the presence of strong built-in electric fields reaching up to 49 kV/cm. It was demonstrated that the spectral density of voltage fluctuations at room temperature was found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual capture defects. Furthermore, varying bias voltage, we considered optimal conditions for device room temperature operation in the THz range with respect to signal-to-noise ratio. The THz detectors grown with beam equivalent pressure In/Ga ratio equal to 2.04 exhibit the minimal level of the low-frequency noise, while InGaAs layers grown with beam equivalent pressure In/Ga ratio equal to 2.06 are found to be well suited for fabrication of room temperature bow-tie THz detectors enabling sensitivity of 13 V/W and noise equivalent power (NEP) of 200 pW/√Hz at 0.6 THz due to strong built-in electric field effects.

Bandlike and localized states of extended defects in n-type In0.53Ga0.47As

In0.53Ga0.47As p + n diodes with different densities of extended defects have been analyzed by detailed structural and electrical characterization. The defects have been introduced during Metal-Organic Vapor Phase Epitaxy (MOVPE) growth by using a lattice-mismatched layer on a semi-insulating InP or GaAs substrate. The residual strain and indium content in the n-type In0.53Ga0.47As layer have been determined by high-resolution X-ray diffraction, showing nearly zero strain and a fixed indium ratio of 0.53. The deep levels in the layer have been characterized by Deep Level Transient Spectroscopy. The mean value of electron traps at 0.17 ± 0.03 eV below the conduction band minimum EC is assigned to the “localized” states of α 60° misfit dislocations; another broad electron trap with mean activation energies between EC− 0.17 ± 0.01 and 0.39 ± 0.04 eV, is identified as threading dislocation segments with “band-like” states. A high variation of the pre-exponential factor KT by 7 orders of magnitude is found for the latter when changing the filling pulse time, which can be explained by the coexistence of acceptor-like and donor-like states in the core of split dislocations in III-V materials. Furthermore, two hole traps at EV+ 0.42 ± 0.01 and EV+ 0.26 ± 0.13 eV are related to the double acceptor of the Ga(In) vacancy (VGa/In3-/2-) and 60° β misfit dislocations, respectively. Finally, the dislocation climbing mechanism and the evolution of the antisite defects AsGa/In are discussed for n-type In0.53Ga0.47As.

Recent progress in terahertz difference-frequency quantum cascade laser sources

Abstract Terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation are currently the only electrically pumped monolithic semiconductor light sources operating at room temperature in the 1–6-THz spectral range. Relying on the active regions with the giant second-order nonlinear susceptibility and the Cherenkov phase-matching scheme, these devices demonstrated drastic improvements in performance in the past several years and can now produce narrow-linewidth single-mode terahertz emission that is tunable from 1 to 6 THz with power output sufficient for imaging and spectroscopic applications. This paper reviews the progress of this technology. Recent efforts in wave function engineering using a new active region design based on a dual-upper-state concept led to a significant enhancement of the optical nonlinearity of the active region for efficient terahertz generation. The transfer of Cherenkov devices from their native semi-insulating InP substrates to high-resistivity silicon substrates resulted in a dramatic improvement in the outcoupling efficiency of terahertz radiation. Cherenkov terahertz QCL sources based on the dual-upper-state design have also been shown to exhibit ultra-broadband comb-like terahertz emission spectra with more than one octave of terahertz frequency span. The broadband terahertz QCL sources operating in continuous-wave mode produces the narrow inter-mode beat-note linewidth of 287 Hz, which indicates frequency comb operation of mid-infrared pumps and thus supports potential terahertz comb operation. Finally, we report the high-quality terahertz imaging obtained by a THz imaging system using terahertz QCL sources based on intra-cavity difference frequency generation.

Photo-conductive detection of continuous THz waves via manipulated ultrafast process in nanostructures

Time-domain and frequency-domain terahertz (THz) spectroscopy systems often use materials fabricated with exotic and expensive methods that intentionally introduce defects to meet short carrier lifetime requirements. In this study, we demonstrate the development of a nano-photomixer that meets response speed requirements without using defect-incorporated, low-temperature-grown (LTG) semiconductors. Instead, we utilized a thin InGaAs layer grown on a semi-insulating InP substrate by metal-organic chemical vapor deposition (MOCVD) combined with nano-electrodes to manipulate local ultrafast photo-carrier dynamics via a carefully designed field-enhancement and plasmon effect. The developed nano-structured photomixer can detect continuous-wave THz radiation up to a frequency of 2 THz with a peak carrier collection efficiency of 5%, which is approximately 10 times better than the reference efficiency of 0.4%. The better efficiency results from the high carrier mobility of the MOCVD-grown InGaAs thin layer with the coincidence of near-field and plasmon-field distributions in the nano-structure. Our result not only provides a generally applicable methodology for manipulating ultrafast carrier dynamics by means of nano-photonic techniques to break the trade-off relation between the carrier lifetime and mobility in typical LTG semiconductors but also contributes to mass-producible photo-conductive THz detectors to facilitate the widespread application of THz technology.

Lasing characteristics of 1.3-µm npn-AlGaInAs transistor-laser with narrower-bandgap p-GaInAsP base layer on semi-insulating InP substrate

A 1.3-µm npn-AlGaInAs transistor laser (TL) on Fe-doped semi-insulating (SI) InP substrate is realized for the first time with improved lasing characteristics by adopting a p-GaInAsP base layer with narrower bandgap and a 4-µm-thick Au electrode. The narrower bandgap is introduced to improve a current gain. The 4-µm-thick Au electrode is introduced to improve thermal characteristics by electrolytic plating. A current gain of 0.27, which is 1.5 times higher than that in our previous report, can be achieved due to the narrower bandgap. Moreover, lasing operation up to 40 °C that is attributed to the lower thermal resistance of the device is achieved by Au plating. The thermal resistance of a TL with Au plating is 20% lower than that of a TL without Au plating, and the temperature is the highest temperature operation for 1.3-µm TL.

Broadly tunable terahertz difference-frequency generation in quantum cascade lasers on silicon

We report broadly tunable terahertz (THz) sources based on intracavity Cherenkov difference-frequency generation in quantum cascade lasers transfer-printed on high-resistivity silicon substrates. Spectral tuning from 1.3 to 4.3 THz was obtained from a 2-mm long laser chip using a modified Littrow external cavity setup. The THz power output and the midinfrared-to-THz conversion efficiency of the devices transferred on silicon are dramatically enhanced, compared with the devices on a native semi-insulating InP substrate. Enhancement is particularly significant at higher THz frequencies, where the tail of the Reststrahlen band results in a strong absorption of THz light in the InP substrate.

Terahertz difference-frequency quantum cascade laser sources on silicon

Terahertz quantum cascade laser sources based on intra-cavity frequency mixing are currently the only monolithic electrically pumped semiconductor devices that can operate in the 1–6 THz spectral range at room temperature. The introduction of the Cherenkov waveguide scheme in these devices grown on semi-insulating InP substrates enabled generation of tens of microwatts of average terahertz power output and wide spectral tunability. However, terahertz radiation outcoupling in these sources is still highly inefficient. Here we demonstrate that an application of the III–V-on-silicon hybrid laser concept to terahertz quantum cascade laser sources based on Cherenkov intra-cavity difference-frequency generation dramatically improves their output power and mid-infrared-to-terahertz conversion efficiency. The best-performing device transfer-printed on a float-zone high-resistivity silicon substrate produced 270 μW of peak power output at 3.5 THz at room temperature, a factor of 5 improvement over the best reference devices on a native semi-insulating InP substrate.

1.3-μm-Wavelength AlGaInAs Multiple-Quantum-Well Semi-Insulating Buried-Heterostructure Distributed-Reflector Laser Arrays on Semi-Insulating InP Substrate

1.3-μm-wavelength AlGaInAs distributed-reflector laser arrays on semi-insulating InP substrate for high-speed direct modulation are investigated to realize compact and low-power-consumptive optical modules. Combination of AlGaInAs quantum wells with large differential gain and semi-insulating buried-heterostructure for reduction of the volume in active region achieved high-speed direct modulation. The fabricated lasers in the array lase with different wavelengths with stable single-longitudinal mode. Clear eye-opening and large mask margin were obtained in push-pull driving at 25.8 Gb/s direct modulation with coplanar electrode and semi-insulating InP substrate. Comparison of modulation waveform under simultaneous operation of neighbor lasers shows that crosstalk between lasers in the array is small. Clear eye-openings, large mask margins, and 10-km fiber transmission of four different wavelength lasers on LAN-WDM grid are demonstrated under 28-Gb/s operation at 50 °C. For further high-speed operation, 43-Gb/s direct modulation were performed. These results indicate that the 1.3-μm AlGaInAs DR laser arrays are promising as light sources for 100-Gb/s Ethernet and higher speed transmission.

Enhanced optical properties of InAs/InAlGaAs/InP quantum dots grown by metal-organic chemical vapor deposition using a double-cap technique

The effects of a double-cap procedure on the optical properties of an InAs/InAlGaAs quantum dots (QDs) system grown by metal-organic chemical vapor deposition (MOCVD) have been investigated by atomic force microscopy (AFM) and room temperature photoluminescence (RT-PL) spectroscopy. An optimized QD growth condition has been achieved, with an areal density of 4.6×1010cm−2. It was found that the thickness and lattice constant of the high temperature second cap layer (SCL) were crucial for improving the integrated PL intensity and line-width of the 1.55μm emission from the InAs/InAlGaAs QD system grown on a semi-insulating InP (100) substrate. With fine-tuned SCL thickness and lattice constant, the optical performance of the five-stack QDs was enhanced. The improvements can be attributed to the smooth growth front, observed from the AFM images, and the well-balanced stress engineering.

10 Gbps Operation of Top Air-Clad Lateral Junction Waveguide-Type Photodiodes

Toward on-chip photonic integrated circuits (PICs) based on a membrane structure, a lateral junction waveguide-type photodiode fabricated on semi-insulating (SI-) InP substrate was successfully demonstrated. A responsivity of 0.39 A/W was obtained by adopting a bulk GaInAs absorption layer. In addition, a narrow stripe width of 0.85 µm was chosen for the realization of high-speed operation. As a result, a 3 dB bandwidth of 8.8 GHz at a bias voltage of -2 V was attained for a device length of 380 µm, and a clear eye opening was obtained up to 10 Gbps.

Design of Lateral-Current-Injection-Type Membrane Distributed-Feedback Lasers for On-Chip Optical Interconnections

For application to on-chip optical interconnections, lateral-current-injection (LCI) membrane distributed-feedback (DFB) lasers, which are expected to be potential components for such an application, were investigated from the aspects of low threshold current operation and high-speed direct modulation capability. First, the stripe width dependence of the carrier injection delay time was evaluated from small-signal response measurements of LCI Fabry-Perot lasers prepared on a semi-insulating InP substrate, and it was found that a narrower stripe width was advantageous for shorter carrier injection delay time as well as higher internal quantum efficiency. Second, semiconductor core layer thickness dependences of the lasing properties of LCI-membrane-DFB lasers, such as the threshold current, output power, relaxation oscillation frequency, and a 3-dB bandwidth, were investigated theoretically. A strong optical confinement effect in the semiconductor membrane structure enabled the design of an LCI-membrane-DFB laser with a low threshold current of 0.16 mA, an output power of more than 0.16 mW, and a high relaxation oscillation frequency of 8.9 GHz at a bias current of only 1 mA. From these values, the LCI-membrane-DFB laser can be a good candidate for a low-pulse-energy (<;100 fJ/bit) light source, for high-speed (>10 Gb/s) transmission, and for on-chip optical interconnections.

Improvement of the surface quality of semi-insulating InP substrates through a novel etching and cleaning method

Residual impurities and contamination on semi-insulating (SI) InP wafers are detrimental for epitaxial growth and device performance, especially because residual silicon on an SI-InP wafer surface is electrically active and generates an n-type conduction layer at the interface between the epilayer and the InP substrate. In order to reduce the concentration of Si and improve surface quality, the authors investigate a wet-chemical cleaning process for ready-to-use InP substrates. A novel and practical cleaning process was developed by adding an alkaline solution to the conventional acidic cleaning process. Time-of-flight secondary mass spectrometry, a very powerful analysis technique to characterize surfaces and investigate any organic and inorganic contamination present on the InP surface, was used after the samples were etched under different cleaning processes. The results show that the novel etching process effectively reduces the Si contamination.

Enhanced room temperature electronic and thermoelectric properties of the dilute bismuthide InGaBiAs

We report room temperature electronic and thermoelectric properties of Si-doped In0.52Ga0.48BiyAs1−y with varying Bi concentrations. These films were grown epitaxially on a semi-insulating InP substrate by molecular beam epitaxy. We show that low Bi concentrations are optimal in improving the conductivity, Seebeck coefficient, and thermoelectric power factor, possibly due to the surfactant effects of bismuth. We observed a reduction in thermal conductivity with increasing Bi concentration, which is expected because of alloy scattering. We report a peak ZT of 0.23 at 300 K.