A Practical Backside Technology for Indium Phosphide MMICs

A wet etching process for backside via holes suitable for use on InP MMICs technologies is developed for indium phosphide substrate.PMMA is used to mount InP wafer onto glass carrier.Spattered Ta film is utilized as etch mask.HCl+H 3PO 4 solution realised a etch until a depth of 100μm.It is demonstrated that the wet etching backside process is controllable with large latitudes.

Surface activation of colloidal indium phosphide nanocrystals

Against general wisdom in crystallization, the nucleation of InP and III-V quantum dots （QDs） often dominates their growth. Systematic studies on InP QDs identified the key reason for this： the dense and tight alkanoate-ligand shell around each nanocrystal. Different strategies were explored to enable necessary ligand dynamics--i.e., ligands rapidly switching between being bonded to and detached from a nanocrystal upon thermal agitation--on nanocrystals to simultaneously retain colloidal stability and allow appreciable growth. Among all the surface-activation reagents tested, 2,4-diketones （such as acetylacetone） allowed the full growth of InP QDs with indium alkanoates and trimethylsilylphosphine as precursors. While small fatty acids （such as acetic acid） were partially active, common neutral ligands （such as fatty amines, organophosphines, and phosphine oxides） showed limited activation effects. The existing amine-based synthesis of InP QDs was activated by acetic acid formed in situ. Surface activation with common precursors enabled the growth of InP QDs with a distinguishable absorption peak between ~450 and 650 nm at mild temperatures （140-180 ~C）. Furthermore, surface activation was generally applicable for InAs and III-V based core/shell QDs.

Past,present and future of indium phosphide quantum dots

Indium phosphide(InP)colloidal quantum dots(QDs)have been drawn significant attention as a potentially less toxic alternative to cadmium-based QDs over the past two decades.The advances in their colloidal synthesis methods have allowed for the synthesis of a wide variety of compositions,heterojunctions,dopants,and ligands that enabled spectral tunability from blue to near-infrared,narrow emission linewidths,and perfect quantum yields approaching unity.Furthermore,it has higher covalency compared to cadmium chalcogenides leading to improved optical stability.The state-of-the-art InP QDs with appealing optical and electronic properties have excelled in many applications such as light-emitting diodes,luminescent solar concentrators(LSCs),and solar cells with high potential for commercialization.This review focuses on the history,recent development,and future aspect of synthesis and application of colloidal InP QDs.

Investigation of Residual Donor Defects in Undopedan d Fe-Doped LEC InP

The free electron concentration of as-grown liquid encapsulated Czochralski (LE C) InP measured by Hall effect is much higher than the concentration of net dono r impurity determined by glow discharge mass spectroscopy.Evidence of the existe nce of a native donor hydrogen-indium vacancy complex in LEC undoped and Fe-do ped InP materials can be obseved with infrared absorption spectra.The concentra tion increase of the donor complex correlates with the increase of ionized deep acceptor iron impurity Fe concentration in Fe-doped semi-insulating (S I) InP.These results indicate that the hydrogen-indium vacancy complex is an im portant donor defect in as-grown LEC InP,and that it has significant influence on the compensation in Fe-doped SI InP

Preparation of Semi-Insulating Material by Annealing Undoped InP

Semi insulating (SI) InP wafers of 50 and 75mm in diameter can be obtained by annealing of undoped liquid encapsulated Czochralski (LEC) InP at 930℃ for 80h.The annealing ambient can be pure phosphorus (PP) or iron phosphide (IP).The IP SI InP wafers have good electrical parameters and uniformity of whole wafer.However,PP SI InP wafers exhibit poor uniformity and electrical parameters.Photoluminescence which is subtle to deep defect appears in IP annealed semi insulating InP.Traps in annealed SI InP are detected by the spectroscopy of photo induced current transient.The results indicate that there are fewer traps in IP annealed undoped SI InP than those in as grown Fe doped and PP undoped SI InP.The formation mechanism of deep defects in annealed undoped InP is discussed.

Electrical Transport Properties of Annealed Undoped InP

The electrical properties of annealed undoped n type InP are studied by temperature dependent Hall effect (TDH) and current voltage ( I V ) measurements for semiconducting and semi insulating samples,respectively.Defect band conduction in annealed semiconducting InP can be observed from TDH measurement,which is similar to those of as grown unintentionally doped InP with low carrier concentration and moderate compensation.The I V curves of annealed undoped SI InP exhibit ohmic property in the applied field region up to the onset of breakdown.Such a result is different from that of as grown Fe doped SI InP which has a nonlinear region in I V curve explained by the theory of space charge limited current.

Recent progress in integrated electro-optic frequency comb generation

Optical frequency combs have emerged as an important tool enabling diverse applications from test-and-measurement,including spectroscopy,metrology,precision distance measurement,sensing,as well as optical and microwave waveform synthesis,signal processing,and communications.Several techniques exist to generate optical frequency combs,such as mode-locked lasers,Kerr micro-resonators,and electro-optic modulation.Important characteristics of optical frequency combs include the number of comb lines,their spacing,spectral shape and/or flatness,and intensity noise.While mode-locked lasers and Kerr micro-resonators can be used to obtain a large number of comb lines compared to electro-optic modulation,the latter provides increased flexibility in tuning the comb spacing.For some applications in optical communications and microwave photonics,a high degree of integration may be more desirable over a very large number of comb lines.In this paper,we review recent progress on integrated electro-optic frequency comb generators,including those based on indium phosphide,lithium niobate,and silicon photonics.

Development of a simple two-step lithography fabrication process for resonant tunneling diode using air-bridge technology

This article reports on the development of a simple two-step lithography process for double barrier quantum well(DBQW)InGaAs/AlAs resonant tunneling diode(RTD)on a semi-insulating indium phosphide(InP)substrate using an air-bridge technology.This approach minimizes processing steps,and therefore the processing time as well as the required resources.It is particularly suited for material qualification of new epitaxial layer designs.A DC performance comparison between the proposed process and the conventional process shows approximately the same results.We expect that this novel technique will aid in the recent and continuing rapid advances in RTD technology.

Notch-δ-doped InP Gunn diodes for low-THz band applications

The viability of the indium phosphide(InP)Gunn diode as a source for low-THz band applications is analyzed based on a notch-δ-doped structure using the Monte Carlo modeling.The presence of theδ-doped layer could enhance the current harmonic amplitude(A0)and the fundamental operating frequency(f0)of the InP Gunn diode beyond 300 GHz as compared with the conventional notch-doped structure for a 600-nm length device.With its superior electron transport properties,the notch-δ-doped InP Gunn diodes outperform the corresponding gallium arsenide(GaAs)diodes with up to 1.35 times higher in f0 and 2.4 times larger in A0 under DC biases.An optimized InP notch-δ-doped structure is estimated to be capable of generating 0.32-W radio-frequency(RF)power at 361 GHz.The Monte Carlo simulations predict a reduction of 44%in RF power,when the device temperature is increased from 300 K to 500 K;however,its operating frequency lies at 280 GHz which is within the low-THz band.This shows that the notch-δ-doped InP Gunn diode is a highly promising signal source for low-THz sensors,which are in a high demand in the autonomous vehicle industry.

Layer Combination Effect on Band Gap Shift of InGaAsP/InP MQWs by Impurity-free Vacancy Disordering

InGaAsP/InP multiple quantum wells with quantum well intermixing have been prepared by impurity-free vacancy disordering.The luminescent characteristics were investigated using photoluminescence and photoreflectance,from which the band gap blue shift was observed.Si3N4,SiO2 and SOG were used for the dielectric layer to enhance intermixing from the outdiffusion of group III atoms.All samples were annealed by rapid thermal annealing.The results indicate that the band gap blue shift varies with the dielectric layers and the annealing temperature.The SiO2 capping with an InGaAs cladding layer was successfully used to induce larger band tuning effect in the InGaAsP/InP MQWs than the Si3N4 capping with an InGaAs cladding layer.On the other hand, samples with the Si3N4-InP cap layer combination also show larger energy shifts than that with SiO2-InP cap layer combination.

Bright InP quantum dots by Ga-doping for red emitters

Environment-friendly indium phosphide(InP)-based quantum dots(QDs)with efficient red-emitting properties are sufficiently needed to satisfy the requirement of burgeoning display and lighting technology.Currently,the syntheses of InP QDs using tris(trimethylsilyl)phosphine as the precursor are highly toxic and expensive.Herein,we successfully introduced gallium(Ga)ions into tris(dimethylamino)phosphine-based red InP cores through thermally-promoted cation exchange,and the obtained Ga-doped InP cores exhibited significantly increased photoluminescence quantum yields(PLQY)of up to 26%.The existence of Ga was directly confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy,and the functions of Ga were systematically studied.After subsequent coating of Ga-doped InP cores with ZnSeS and ZnS shells,the resulting Ga-InP/ZnSeS/ZnS QDs achieved a high PLQY of 62%with an emission maximum at 640 nm.In contrast,without Ga-doping,the PLQY only attained 36%using the same synthetic approach.This indicated an approximate 1.7-fold increase in PLQY.The enhancement of photoluminescence was related to the Ga^(3+),as it not only passivated surface defects of InP cores but also reduced core–shell interface stress.The Ga-InP/ZnSeS/ZnS QDs exhibited good stability towards heat treatment and ultraviolet(UV)irradiation.Moreover,the red light-emitting diode(LED)based on Ga-InP/ZnSeS/ZnS QDs performed well in a wide injected current range of 2 to 200 mA,with a maximum power efficiency of 0.68 lm/W.This work showcases Ga-doping through cation exchange as a promising strategy for enhancing the efficiency of InP-based red emitters.

Absorption of light in InP nanowire arrays

An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. These reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire.

Metamorphic In_(0.53)Ga_(0.47)As p-i-n photodetector grown on GaAs substrates by low-pressure MOCVD

Top-illuminated metamorphic In0.53Ga0.47As p-i-n photodetectors are grown on the ultrathin low- temperature InP buffered GaAs substrates. Photodetectors with the 300-nm-thick In0.53Ga0.47As absorption layer show a typical responsivity of 0.12 A/W to 1.55μm optical radiation, corresponding to an external quantum efficiency of 9.6%. Photodetectors with the active area of 50 × 50 （μm） exhibit the -3 dB bandwidth up to 6 GHz. These results are very encouraging for the application of this metamorphic technology to opto-electronic integrated circuit （OEIC） devices.

Exciton recycling via InP quantum dot funnels for luminescent solar concentrators

Luminescent solar concentrators (LSC) absorb large-area solar radiation and guide down-converted emission to solar cells for electricity production. Quantum dots (QDs) have been widely engineered at device and quantum dot levels for LSCs. Here, we demonstrate cascaded energy transfer and exciton recycling at nanoassembly level for LSCs. The graded structure composed of different sized toxic-heavy-metal-free InP/ZnS core/shell QDs incorporated on copper doped InP QDs, facilitating exciton routing toward narrow band gap QDs at a high nonradiative energy transfer efficiency of 66%. At the final stage of non-radiative energy transfer, the photogenerated holes make ultrafast electronic transitions to copper-induced mid-gap states for radiative recombination in the near-infrared. The exciton recycling facilitates a photoluminescence quantum yield increase of 34% and 61% in comparison with semi-graded and ungraded energy profiles, respectively. Thanks to the suppressed reabsorption and enhanced photoluminescence quantum yield, the graded LSC achieved an optical quantum efficiency of 22.2%. Hence, engineering at nanoassembly level combined with nonradiative energy transfer and exciton funneling offer promise for efficient solar energy harvesting.

Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas

Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.

High performance 1689-nm quantum well diode lasers

1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers. Stripe width and cavity length of the laser were 1.8 and 300μm, respectively. After being cavity coated and transistor outline （TO） packaged, the lasers showed high performance in practice. The threshold current was about 13 ± 4 mA, the operation current and the lasing spectrum were about 58 ± 6 mA and 1689 ± 6 nm at 6-mW output power, respectively. Moreover, the maximum output power of the lasers was above 20 roW.

Recent advances in development of vertical-cavity based short pulse source at 1.55 μm

This paper reviews and discusses recent developments in passively mode-locked vertical external cavity surface emitting lasers （ML-VECSELs） for short pulse generation at 1.55 gin. After comparing ML- VECSELs to other options for short pulse generation, we reviewed the results of ML-VECSELs operating at telecommunication wavelength and point out the chal- lenges in achieving sub-picosecond operation from a ML- VECSEL at 1.55 gm. We described our recent work in the VECSELs and semiconductor saturable absorber mirrors （SESAMs）, their structure design, optimization and characterization, with the goal of moving the pulse width from picosecond to sub-picosecond.