Ion-implanted GaAs Research Articles

Evaluation of carrier density and mobility in Mn ion-implanted GaAs:Zn nanowires by Raman spectroscopy

The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.

Spectral response characteristics of novel ion-implanted planar GaAs blocked-impurity-band detectors in the terahertz domain

Spectral response characteristics of novel planar GaAs blocked-impurity-band (BIB) detector with the absorption region formed by ion implantation have been investigated. Processing technology and simulation method are described in detail. For obtaining a deep and flat implantation region, four-time-implantation scheme with different implantation energy and dose is proposed. Our results show that the novel planar GaAs BIB detector can response radiations with wavelength range from 165 to 400 μm, corresponding to frequency range from 750 GHz to 1.8 THz, which is perfectly suitable for the security application. An empirical formula is proposed to predict the dependence of spectral width on the depth of absorption region. It is demonstrated that a trade-off between responsivity and dark current has to be made for the optimal depth of absorption region.

Plasmonics in semiconductors and in Ag submicron wires and graphene

Some 50 years ago discussions of plasmonics in semiconductors lead to many new concepts such as travelling domain structures with applications leading even to logic systems. Now plasmonics of submicron wires of Ag and graphene bring new device concepts for the fabrication of compact THz sources and optical focusing of the beat signal into the active area. Here as an experimental example such new opportunities are involved with compact THz sources based on optical laser mixing. They include resonant plasmonic structures at THz and optical frequencies to locally enhance the electromagnetic fields at THz as well as optical frequencies by the combination of semiconductor-graphene plasmons respectively by the semiconductor-metal-nanostructure plasmons. Of particular interest is the usage of graphene, which is optically transmitting and which is either a semimetal or can be transformed into a semiconductor by reducing the width of its strips to about 30 nm, opening a band gap in the meV to tens of the meV range. A successful experimental structure for continuous-wave THz photomixing is fabricated using 1D and 2D nanocontacts either on low-temperature-grown (LTG) GaAs or on nitrogen ion-implanted (N+i) GaAs and graphene sheets. The overlaying 1D and 2D nanocontacts were formed by silver nanowires with a diameter of 60 or 120 nm. They can handle currents of >10 and >30 mA, respectively, without electromigration enabling reliably high photocurrents and field enhancement at THz frequencies by plasmonic effects. The nanomaterial structurization in connection with present-day plasmonic applications is now to be discussed in a similar manner as past opportunities with semiconductor plasmonics.

Development of technology of multicharged ion implantation of GaAs for submicron structures of large-scale integrated circuits

Розроблена технологія виготовлення іонно-легованих структур GaAs. Імплантація іонів кремнію, берилію, цинку проводилась в підкладку із напівізолюючого арсеніду галію марки АГЧП-2а. Імплантація домішки через капсулююче покриття дозволило отримати досить високі значення рухливості носіїв струму в каналах польового транзистора Шотткі (ПТШ), що дозволяє формувати на них КМОН-структури. Застосування багатозарядної імплантації та імпульсного фотонного відпалу для активації n + -областей витоку і стоку забезпечило рівень ретроградного легування стік-витокових контактів на рівні (2–5)·10 18 см -3 .

Dielectric Function of Native Oxide on Ion-Implanted GaAs

Dielectric Function of Native Oxide on Ion-Implanted GaAs M. Kulika,∗, W. Rzodkiewicz, Š. Gluba and A.P. Kobzev Institute of Physics, Maria Curie-Skaodowska University, pl. M. Curie-Skaodowskiej 1, 20-031 Lublin, Poland Institute of Electron Technology, al. Lotnikow 32/46, 02-668 Warszawa, Poland Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Joliot-Curie 6 141980 Dubna, Moscow region, Russia

Analytical modelling of the current ( I )–voltage ( V ) characteristics of sub‐micron gate‐length ion‐implanted GaAs MESFETs under dark and illuminated conditions

An analytical model for current (I)–voltage (V) characteristics of a short-channel ion-implanted GaAs MESFET has been presented for dark and illuminated conditions. For the sake of simplicity, the non-analytic (i.e. non-integral) Gaussian doping function commonly considered for the channel doping of an ion-implanted GaAs metal semiconductor field effect transistor (MESFET) has been replaced by an analytic Gaussian-like doping profile in the vertical direction. The device uses an indium–tin oxide-based Schottky gate through which an optical radiation of 0.87 μm wavelength is coupled from an external source into the device to modulate the I–V characteristics of the short-gate length GaAs MESFET. The coupled light generates electron–hole pairs in the active channel region below the gate and develops a photovoltage across the Schottky gate–channel junction and modulates the device characteristics. This study also includes the modelling of this photovoltaic effect by taking the short-gate length effects into consideration. The developed model includes the effects of doping profile and device parameters on the drain current of the short-channel ion-implanted GaAs MESFETs under dark and illuminated conditions of operations. The accuracy of the proposed model is extensively verified by comparing the theoretically predicted results with numerical simulation data obtained by using the commercially available ATLASTM device simulation software.

Hopping Conduction in Mn Ion-Implanted GaAs Nanowires

We report on temperature-dependent charge transport in heavily doped Mn(+)-implanted GaAs nanowires. The results clearly demonstrate that the transport is governed by temperature-dependent hopping processes, with a crossover between nearest neighbor hopping and Mott variable range hopping at about 180 K. From detailed analysis, we have extracted characteristic hopping energies and corresponding hopping lengths. At low temperatures, a strongly nonlinear conductivity is observed which reflects a modified hopping process driven by the high electric field at large bias.

The influence of a doping profile on the characteristics of an ion-implanted GaAs field-effect transistor with a Schottky barrier

A GaAs field-effect ion-implanted transistor with a Schottky barrier is simulated. The doping profile obtained when doping through an insulator mask is determined and the dependences of the static transistor characteristics on the parameters of the doping profile are calculated and analyzed. The physical processes controlling the transistor characteristics in the case of a variation in the parameters of its doping profile and the coefficient of compensation of the substrate are studied. Based on calculations, the optimal doping-profile parameters ensuring the best characteristics for transistors are predicted.

A Two-Dimensional (2D) Analytical Model for the Potential Distribution and Threshold Voltage of Short-Channel Ion-Implanted GaAs MESFETs under Dark and Illuminated Conditions

A two-dimensional (2D) analytical model for the potential distribution and threshold voltage of short-channel ion-implanted GaAs MESFETs operating in the sub-threshold regime has been presented. A double-integrable Gaussian-like function has been assumed as the doping distribution profile in the vertical direction of the channel. The Schottky gate has been assumed to be semi-transparent through which optical radiation is coupled into the device. The 2D potential distribution in the channel of the shortchannel device has been obtained by solving the 2D Poisson’s equation by using suitable boundary conditions. The effects of excess carrier generation due to the incident optical radiation in channel region have been included in the Poisson’s equation to study the optical effects on the device. The potential function has been utilized to model the threshold voltage of the device under dark and illuminated conditions. The proposed model has been verified by comparing the theoretically predicted results with simulated data obtained by using the commercially available ATLAS™ 2D device simulator.

A two-dimensional analytical model for the gate–source and gate–drain capacitances of ion-implanted short-channel GaAs metal-semiconductor-field effect transistor under dark and illuminated conditions

This paper presents an analytical model for the internal capacitances of short-channel ion-implanted GaAs MESFETs under dark and illuminated conditions. The device structure considered in this study is a normally-on self-aligned GaAs MESFET with indium tin oxide (ITO) as the Schottky metal for the gate electrode of the device. The gate area of the device is illuminated by an optical radiation of 0.87 μm from an external source which is coupled into the device through the semitransparent ITO metal at Schottky-gate to modulate the electrical and microwave characteristics of the device. The nonanalytic Gaussian doping profile commonly considered for the channel doping of an ion-implanted GaAs MESFET has been replaced by an analytic Gaussianlike function for the simplicity of the present model. The two-dimensional (2D) potential distribution obtained by solving the 2D Poisson’s equation by including the effect of photo-generated carriers due to the incident optical radiation has been utilized to model the depletion region width below the gate of the short-channel GaAs MESFETs. The depletion width model has then been used to model the internal gate-source and gate-drain capacitances of the device operating under both the linear and saturation regions. The effect of illumination on the Schottky junction at the gate of the MESFET has been modeled by considering an induced photo-voltage developed across the junction that is superimposed on the applied gate bias voltage. The proposed model has been verified by comparing the theoretically predicted results with simulated data obtained by using the commercially available ATLASTM 2D device simulator.

Blister formation in ion-implanted GaAs: Role of diffusivity

We have investigated the influence of substrate temperature during implantation, Timplant, on blister formation in GaAs:N layers produced by N ion implantation followed by rapid thermal annealing. Similar depths of popped blisters (craters) and damage profiles were observed for both low and high Timplant. This is in contrast to reports of Timplant-dependent blister formation in higher-diffusivity systems such as GaAs:H and Si:H. The apparent Timplant-insensitivity of blister formation in GaAs:N is likely due to the lower diffusivity of N in GaAs in comparison to that of H in GaAs and Si.

Influence of activation of Si29+ ion-implantation in GaAs on ohmic contact resistance and electrical performances of MESFETs

The active layers of Metal Semiconductor Field Effect Transistors (MESFETs) are obtained by Si29+ ion implantation in GaAs. Implantation was done at 35 keV with a higher dose near the wafer surface for facilitating easier formation of ohmic contacts, and at 180 keV with a lower dose for obtaining the device channel. Post-implantation annealing was carried out in a rapid thermal processor for activating the implants. Very high activation levels of about 60% for the n+ GaAs layer, and 85% for the n-GaAs channel layer were achieved by annealing at 955 °C for 25 s. Activation was characterized using C–V profiling, secondary ion mass spectrometry and by electrical device data of fabricated MESFETs. We attempt an experimental correlation between the ohmic contact resistance (R c) and activation of both the n+ and the channel layer. It was found that very high and simultaneous activation of the n+ and channel layers results in very low contact resistances. The conduction of source-drain current into the channel is easily facilitated due to reduction in the resistance of the transition region at the interface of n+-contact and n-channel layers.

Terahertz photomixing in high energy oxygen- and nitrogen-ion-implanted GaAs

In this letter, the authors elaborate a detailed study of ion-implanted GaAs terahertz photomixers. The authors implanted several GaAs samples with oxygen and nitrogen ions with energies between 2 and 3MeV and doses ranging from 2×1011to3×1013cm−2. The samples were processed by patterning metal-semiconductor-metal structures on the feed point of self-complementary log-periodic spiral broadband antennas. From dc measurements and analysis of frequency roll-off in the 100GHz–1THz range under variable bias conditions, the authors studied systematically the carrier trapping time, terahertz power, and photocurrent dependence on applied voltage and frequency for the different samples.

Terahertz continuous-wave large-area traveling-wave photomixers on high-energy low-dose ion-implanted GaAs

Nitrogen ion implantation at 3MeV and low doses into commercial semi-insulating GaAs (107Ωcm) is used to manufacture continuously operated metal-semiconductor-metal terahertz photomixer radiation sources based on a traveling-wave interdigitated-finger coplanar stripline structure. The authors systematically investigated the terahertz efficiency over the implantation dose range of 5.6×1011–1.8×1013ions∕cm2 and determined the optimum implantation dose range for operation in the frequency range 500–1000GHz, where a significant higher efficiency is obtained compared to low-temperature-grown GaAs.

Annealing Induced Diffusion Dynamics in As Ion-Implanted GaAs

Annealing Induced Diffusion Dynamics in As Ion-Implanted GaAs

Radical-beam gettering epitaxy of GaN layers on nitrogen-ion-implanted GaAs substrates

Thin GaN films have been grown on N+-ion-implanted single-crystal GaAs(111) substrates by radical-beam gettering epitaxy, and their structural perfection has been assessed by high-resolution x-ray diffraction. At growth temperatures from 770 to 970 K, the layers consist of hexagonal GaN and have mirror-smooth surfaces. Nitrogen-ion implantation into the substrate favors the formation of a sharp film/substrate interface owing to radiation-enhanced gallium diffusion. Analysis of the GaN/GaAs structures by Auger electron and x-ray photoelectron spectroscopies in combination with depth profiling indicates that the GaN layer is enriched in gallium. The N: Ga atomic ratio in the films is 0.98: 1, which is attributable to radiation-enhanced gallium diffusion.

Terahertz emission properties of arsenic and oxygen ion-implanted GaAs based photoconductive pulsed sources

In this work we compare the characteristics of asymmetrically excited small-aperture antenna-type pulsed terahertz emitters fabricated using an ion implantation process. Our photoconductive materials consist of high resistivity GaAs substrates. Multienergy implantations of arsenic (1.2 and 2MeV) and oxygen (180, 450, and 700keV) have been used to obtain an almost uniform density of vacancies over the optical absorption depth in bulk GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort laser pulses. Ion implantation followed by a thermal annealing process introduces nonradiative centers in our substrates which reduce the carrier lifetime and modify the shape of our terahertz pulses. Results obtained as functions of the laser excitation power and bias voltage are discussed and a comparison of the performance of these devices with conventional small-aperture antennas is given.

Carrier recombination properties in low-temperature-grown and ion-implanted GaAs

Electron and hole trapping times, electron mobilities were investigated in low-temperature-grown GaAs (LTG GaAs) and GaAs crystals implanted by four different ion species. Optical pump – THz probe and recently developed optical pump – mid-IR probe techniques have been used in these experiments. Recombination parameters of the investigated materials were estimated in point of view of possible applications of these materials in THz radiation devices. It has been concluded that LTG GaAs is preferable material for pulse THz applications because of its shorter electron trapping times and higher electron mobility. However, the hole trapping time in ion-implanted material is shorter than in LTG GaAs, making it a suitable for devices working in cw-mode, e. g. THz photomixers. The shortest carrier trapping times and the largest electron mobility were found for O-implanted GaAs.

Low-Temperature MBE Grown GaAs for Pulsed THz Radiation Applications

The coherent generation and detection of terahertz (THz) radiation using ultrashort laser pulses and photoconductive antennae have been intensively studied during the last decade. The best results were achieved when low-temperature MBE grown GaAs (LTG GaAs) or ion-implanted GaAs layers were used as a basis for THz emitters and detectors. The ultimate performance of these devices depends on carrier mobilities and their trapping times in semiconductor layers; therefore the determination of those parameters is of a critical importance. In the present work, we will describe the characterization of GaAs layers with ultrafast carrier recombination and the results obtained on THz radiation components manufactured from these layers.

Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission

We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both experimentally and using a three-dimensional carrier dynamics simulation. A uniform density of vacancies was formed over the optical absorption depth of bulk GaAs samples by performing multi-energy implantations of arsenic ions (1 and 2.4MeV) and subsequent thermal annealing. In a series of THz emission experiments the frequency of peak THz power was found to increase significantly from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to 10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast carrier dynamics to reproduce and explain these results. The effect of the ion-induced damage was included in the simulation by considering carrier scattering at neutral and charged impurities, as well as carrier trapping at defect sites. Higher vacancy concentrations and shorter carrier trapping times both contributed to shorter simulated THz pulses, the latter being more important over experimentally realistic parameter ranges.