Si Donors Research Articles

300 mm InGaAs-on-insulator substrates fabricated using direct wafer bonding and the Smart Cut™ technology

This paper reports the first demonstration of 300 mm In0.53Ga0.47As-on-insulator (InGaAs-OI) substrates. The use of direct wafer bonding and the Smart Cut™ technology lead to the transfer of high quality InGaAs layer on large Si wafer size (300 mm) at low effective cost, taking into account the reclaim of the III–V on Si donor substrate. The optimization of the three key building blocks of this technology is detailed. (1) The III–V epitaxial growth on 300 mm Si wafers has been optimized to decrease the defect density. (2) For the first time, hydrogen-induced thermal splitting is made inside the indium phosphide (InP) epitaxial layer and a wide implantation condition ranges is observed on the contrary to bulk InP. (3) Finally a specific direct wafer bonding with alumina oxide has been chosen to avoid outgas diffusion at the alumina oxide/III–V compound interface.

Study of optical properties of bulk GaN crystals grown by HVPE

We investigated the optical properties of a series of GaN samples sliced from the same bulk crystal grown using hydride vapor phase epitaxy. The high crystalline quality of the samples was evaluated using cathodoluminescence measurements, and the dislocation density ranged from 2.4 × 106 to 2.3 × 105 cm−2. The impurity concentration was determined using secondary-ion mass spectroscopy, and photoluminescence (PL) measurements were conducted in the range of 3–300 K. We did not find a correlation between the O or C impurities and the weak yellow luminescence (YL) band. As the dislocation density decreased, the intensity of the band edge emission increased and that of the YL band decreased. A competition between the two-electron satellite lines correlated to Si and the YL band was also observed in the low-temperature PL spectra, which demonstrated that the Si impurity also plays an important role in the weak YL band of these GaN samples. These results indicate that the Si donors around the dislocations, as reasonable sources of shallow donors, will recombine with possible deep acceptors and finally respond with the YL.

Low-leakage current and high-breakdown voltage GaN-on-Si (111) System with an AlGaN impurity blocking layer

The influence of different AlGaN Impurity Blocking Layer (IBL) thickness in the GaN/Si (111) structure with GaN/AlN SLs buffer on the material and electrical properties of GaN/Si (111) system was studied in detail. It is found that the insertion of AlGaN IBL can increase the (102) FWHM and decrease the (002) FWHM. Meanwhile, AlGaN IBL with an optimized thickness can further improve the surface roughness and strain-state of GaN-Si (111) system. By using Secondary Ion Mass Spectroscopy, it is found that AlGaN IBL have a strong effect in blocking the Si donor impurities originating from the Si substrate during the high temperature growth, which can decrease the leakage current while the breakdown voltage can be dramatically increased.

Single shot spin readout using a cryogenic high-electron-mobility transistor amplifier at sub-Kelvin temperatures

We use a cryogenic high-electron-mobility transistor circuit to amplify the current from a single electron transistor, allowing for demonstration of single shot readout of an electron spin on a single P donor in Si with 100 kHz bandwidth and a signal to noise ratio of ∼9. In order to reduce the impact of cable capacitance, the amplifier is located adjacent to the Si sample, at the mixing chamber stage of a dilution refrigerator. For a current gain of ∼2.7×103, the power dissipation of the amplifier is 13 μW, the bandwidth is ∼1.3 MHz, and for frequencies above 300 kHz the current noise referred to input is ≤70 fA/Hz. With this amplification scheme, we are able to observe coherent oscillations of a P donor electron spin in isotopically enriched 28Si with 96% visibility.

Influence of the additional p+ doped layers on the properties of AlGaAs/InGaAs/AlGaAs heterostructures for high power SHF transistors

The peculiarities of a new type of pseudomorphic AlGaAs/InGaAs/AlGaAs heterostructures with the additional acceptor doping of barriers used for the creation of the power SHF pseudomorphic high electron mobility transistor (pHEMT) have been studied. A comparison of the transport characteristic of the new and typical pHEMT heterostructures was carried out. The influence of the doped acceptor impurities in the AlGaAs barriers of the new pHEMT heterostructure on the transport properties was studied. It was shown that the application of the additional p+ doped barrier layers allows the achievement of a double multiplex increase in the two-dimensional electron gas (2DEG) concentration in the InGaAs quantum well with no parasite parallel conductivity in the AlGaAs barrier layers. An estimation of the concentration of the doped donors and acceptors penetrating into the deliberately undoped InGaAs quantum well from the AlGaAs barriers was performed by second ion mass spectrometry and photoluminescence spectrometry methods. Taking into account the electron scattering by the ionized impurity atoms, calculation of the electron mobility in the InGaAs channel showed that some reduction of the electron mobility results from scattering by the ionized Si donor due to an increase in the Si concentration and, therefore, is not caused by the application of additional p+ doped layers in the construction of pHEMT heterostructures.

Design and simulation of betavoltaic angle sensor Based on 63Ni–Si

A theoretical design and simulation of betavoltaic angle sensor (beta-AS) based on 63Ni–Si using MCNP code is presented in this article. It can measure the full angle of 0–360° in the temperature range of 233–353K. Beta-AS is composed of semicircular 63Ni as the beta source, which rotates along the circular (four-quadrant) surface of Si as a semiconductor (in p–n structure), so that the change in the source angle in relation to Si surface can be measured based on the changes in Voc observed in each quadrant of Si. For better performance, characteristics of Si and 63Ni have been optimized: ND and NA values of 8e19 and 4e18cm−3 (donor and acceptor doping concentration in Si, respectively), source thickness and activity of 1.5µm and 18mCi, respectively. The relation between angle and Voc is also investigated. The maximum difference between measured and real values of angle (the worst case, i.e., 0.18° for the angle of 45°) occurs at 233K. It has been shown that sensitivity of the sensor decreases with an increase of angle. The results also show that the change in activity does not affect the sensitivity.

Quantitative analysis of electrically detected Ramsey fringes in P-doped Si

This work describes detection of the laser preparation and subsequent coherent manipulation of the quantum states of orbital levels of donors in doped Si, by measuring the voltage drop across an irradiated Si sample. This electrical signal, which arises from thermal ionization of excited orbital states, and which is detected on a millisecond time scale by a voltmeter, leads to much more sensitive detection than can be had using optical methods, but has not before been quantitatively described from first principles. We present here a unified theory which relates the voltage drop across the sample to the wave function of the excited donors, and compare its predictions to experiments in which pairs of picosecond pulses from the Dutch free-electron laser FELIX are used to resonantly and coherently excite P donors in Si. Although the voltage drop varies on a millisecond time scale we are able to measure Ramsey oscillation of the excitation on a picosecond time scale, thus confirming that the donor wave function, and not just its excited state population, is crucial in determining the electrical signal. We are also able to extract the recombination rate coefficient to the ground state of the donor as well as the photoionization cross section of the excited state and phonon induced thermal ionization rate from the excited state. These quantities, which were previously of limited interest, are here shown to be important in the description of electrical detection, which, in our unoptimized configuration, is sensitive enough to enable us to detect the excitation of $\ensuremath{\sim}{10}^{7}$ donors.

Electric field effect on the donor levels bound to the X-valleys in AlAs/GaAs quantum wells

We study the Si donor states bound to X-valleys in a GaAs/AlAs/GaAs layer system in the presence of the electric field using a simple Koster–Slater impurity model. The multilayer structure is modeled with the spds⁎ tight binding approximation and the impurity is described by a single site potential. By analyzing the local density of states we have obtained the values of the binding energies of impurity levels bound to “parallel” Xz and “perpendicular” Xx,y valleys (with respect to the direction of the electric field) as function of barrier width and impurity position in the barrier for various values of the electric field. For the case of zero electric field we have obtained very similar results to the k·p calculations in Carneiro and Weber [1].

(Invited) AlGaN Higher Power Devices

The maximum power that GaN and SiC devices can routinely handle with their present designs is ~105 watts. This is determined by the fact that for a given breakdown voltage, VB, the maximum doping level, nmax (for electrons) and therefore the current density, is limited primarily by the critical filed, ξC, and access to the carrier as defined by the donor, ED, or acceptor, EA, depth. To a lesser extent, it is also limited by the carrier – usually the electron – mobility, μn. GaN, and the III-V semiconductors in general, have an advantage over group IV semiconductors in that they usually form continuous alloys so that ξC can be increased incrementally by increasing the fraction of the larger band gap material in the ternary; for the group IV it is Si, SiC, or diamond, and nothing else in between. To a first approximation the energy gap, EG, increases linearly from 3.39 for GaN to 6.2 eV for AlN and ξC from 3.5 to 11.7 V/cm. They actually increase sublinearly with the concentration, and the effects of this will be briefly explored. The carrier of interest is the electron because the depth of the Mg acceptor, which is deep to begin with, increases quite rapidly with the Al concentration. The dopant of interest is the Si donor, which behaves like a hydrogenic atom up to ~80% Al; above this it is thought to form a DX center. ED increases in depth from 32 to ~75 meV up to this Al%, and although this is ~3kT at room temperature, the large density of states in the conduction band enables most of the donors to be ionized. μn does decrease with the Al%, and at 80% Al it is about half the value it is for GaN. However, this deficit is more than made up for by the increased ξC, which has more than doubled. The conductivity also has a higher order dependence on ξC than it does on μn; in the ideal vertical diode it is proportional to ξC 3 and it is only linearly proportional to μn. Utilizing AlGaN creates other issues, especially for the vertical device, which will have to be the structure used because very high power lateral devices would occupy a larger surface area and be more prone to surface breakdown. The higher source and drain contact resistance for AlGaN will be a problem for both lateral and vertical devices, as will be alloy scattering in the 2DEG. It will be difficult to create a vertical structure that can be easily turned on and off be it with a current aperture or a JFET structure. The AlGaN drift region will also contain mismatch dislocations due to its lattice mismatch substrate, and it will be more difficult to confine the majority of dislocations to the interface, as it is done in SiGe devices, because Si and Ge are cubic and have active primary slip systems exposed to a substantial amount of shear. AlN and GaN have the hexagonal wurtzite structure, and neither the primary basal slip system nor the secondary prismatic slip systems have any shear operating on the slip planes so slip, if it occurs, occurs on pyramidal planes which have large critical shear stresses.

(Invited) High Performance III-V-on-Insulator MOSFETs on Si Realized by Direct Wafer Bonding Applicable to Large Wafer Size

MOSFETs using III-V channels with high mobility and low effective mass have been regarded as strongly important for obtaining CMOS under sub 10 nm technology nodes [1, 2]. One of the critical issues to realize III-V MOSFEs is to form high quality III-V films on large size Si wafers. This heterogeneous integration of III-V devices on Si wafers must be explored for realizing high device performance as well as merging electrical and photonic applications on the Si platform. The existing methodologies could have unavoidable drawbacks such as inferior device quality or high cost in comparison with the current Si-based technology. We have already proposed and demonstrated ultrathin-body (UTB) InGaAs- and GaSb-based channel formation on Si substrates by using direct wafer bonding [3-10]. A UTB (3.2 nm InGaAs)/ultrathin buried oxide (UTBOX) (Al2O3(4.4 nm)/SiO2 (3.3 nm))/Si substrate [3] and a UTB quantum well channel (3 nm InGaAs/3 nm InAs/3 nm InGaAs/ UTBOX/Si) substrate [7, 8] have provide superior MOSFET performance due to the high channel material quality. Here, the III-V channels epitaxially-grown on III-V substrates have been transferred to Si substrates, indicating that the wafer size of III-V layers is limited to that of the available III-V host substrates such as InP. As a consequence, this method is not simply applicable to III-V-on-Si substrates with large Si wafer sizes of 300 nm and beyond. In this study, we present InGaAs-on-insulator (-OI) fabrication from an InGaAs layer grown on a Si donor wafer with a III-V buffer layer instead of growth on an InP donor wafer. In this novel DWB technique using a Si donor wafer, InGaAs/InxAl1-xAs/GaAs layers were epitaxially grown on Si substrates first. After Al2O3 atomic layer deposition as a BOX layer, CMP has been carried out for surface smoothing for Al2O3/III-V/Si wafer and wafers were bonded each other. Subsequent wet etching thinned the top Si and the III-V buffer layers, resulting in the formation of InGaAs-OI on Si substrates. While the present demonstration has employed 4-inch Si host substrates, this technology allows us to yield large wafer size scalability of III-V-OI layers up to the Si wafer size of 300 mm with a high film quality and low cost. The high film quality has been confirmed by Raman and photoluminescence spectra. Also, in order to evaluate the electrical properties, InGaAs-OI MOSFETs was fabricated with the same fabrication process as in the present works [5-8]. Here, gate stack was composed of 10 nm Al2O3 and Ta gate metal. S/D was formed by Ni-InGaAs metal S/D. We have confirmed the good ID-VG curves with a subthreshold slope of 100 mV/dec and on/off ratio > 106 for InGaAs-OI MOSFETs with body thickness of 9 nm and LG of 1 μm. The high electron mobility of 1700 cm2/Vs and the mobility enhancement of 3× against Si MOSFETs have been demonstrated. InGaAs-OI MOSFETs fabricated from the Si donor wafer exhibit high mobility comparable to that from the InP donor wafer, indicating that the present wafer fabrication process can realize sufficiently high quality InGaAs-OI on Si wafers with the same level as those obtained from the InP donor wafer. The leakage current of InGaAs-OI MOSFETs fabricated from the Si donor wafer is also found to be uniform and as low as that from the InP donor wafer. As a result, thanks to the change of donor wafers from InP to Si, the present integration scheme of DWB for InGaAs-OI provides excellent wafer scalability up to the Si wafer size > 300 mm with maintaining high device quality. This work was partly supported by the Innovation Research Project on Nano electronics Materials and Structures, and Research and Development Program for Innovative Energy Efficiency Technology from NEDO and JST-CREST. The authors would like to thank Drs. M. Hata, T. Osada, O. Ichikawa, and H. Yamada in Sumitomo Chemical Corporation for their collaborations.

Electrical characterization of Si doped AlN films synthesized by pulsed laser deposition

The electrical properties of thin AlN films doped with Si (AlN:Si) have been investigated. The films were synthesized on Si substrates at 800 °C by pulsed laser deposition in low-pressure nitrogen ambient. The AlN:Si films exhibit non-ohmic I-V characteristics and the current through these films is controlled by space charge limited current. The C-V dependence of metal-insulator-silicon (MIS) structures with AlN:Si films exhibits an excess capacitance around zero bias voltage. This excess capacitance indicates the presence of deep acceptor levels situated at the boundaries of adjacent grains in the AlN:Si films. The Si donor density in the AlN:Si films, estimated from the 1 MHz C-V characteristics, is of the order of 10 18 cm −3 . The impedance measurements of these AlN:Si structures at different test voltage frequencies reveal that the charge transport mechanism is dominated by either thermally-activated hopping or electron tunneling from occupied to nearest unoccupied deep levels.

(Invited) High Performance III-V-on-Insulator MOSFETs on Si Realized by Direct Wafer Bonding Applicable to Large Wafer Size

MOSFETs using III-V channels with high mobility and low effective mass have been regarded as strongly important for obtaining CMOS under sub 10 nm technology nodes. One of the critical issues to realize III-V MOSFEs is to form high quality III-V films on large size Si wafers. In this paper, we present InGaAs-on-insulator (-OI) fabrication from an InGaAs layer grown on a Si donor wafer with a III-V buffer layer instead of growth on a InP donor wafer. This technology allows us to yield large wafer size scalability of III-V-OI layers up to the Si wafer size of 300mm with a high film quality and low cost. The high film quality has been confirmed by Raman and photoluminescence spectra. In addition, the fabricated InGaAs-OI transistors exhibit the high electron mobility of 1700 cm2/V s and uniform distribution of the leakage current, indicating high layer quality with low defect density.

AlGaN devices and growth of device structures

The structure of a number of GaN/AlGaN devices and their associated material growth and processing issues are examined in some detail, and extrapolations are made to predict what the advantages and challenges would accrue for similar AlGaN electrical and optical devices. For RF HEMTs, it is likely that the advantages of the larger breakdown voltage (V B) in an Al Y Ga1−Y N/Al X Ga1−X N AlGaN channel HEMT would be outweighed by the disadvantages of the lower frequency of operation created by the smaller channel mobility when compared to AlGaAs/GaAs HEMTs. The same thing can be said for lateral high-power electronic HEMTs because AlGaN/GaN HEMTs with GaN channels can now be fabricated with V B ~ 2,000 V, which is thought to be the upper voltage limit for them, even when the device structures are grown on Si substrates with its accompanying high dislocation density and bow. However, theory suggests that using Al Y Ga1−Y N/Al X Ga1−X N structures in vertical transistors and AlGaN P–N diodes could enable pulsed power applications such as electric armor because they should be able to handle an order of magnitude more power due to their ten times larger breakdown field in ~80 % Al AlGaN, and the Si donor is still relatively shallow at this Al concentration. The major challenges to achieving these goals are to be able to controllably dope the AlGaN in the mid 1015 cm−3 range, create an AlGaN current blocking layer beneath the Al Y Ga1−Y N/Al X Ga1−X N channel that contains an aperture to the drain, confine most of the mismatch dislocations in the AlGaN layers to near the interface with the GaN or AlN substrate that is parallel to the (0001) plane, and fabricate ohmic contacts to the AlGaN with a specific contact resistance <10−2 Ω cm2. Theoretically, the latter can be achieved using polarization doping. For applications to optical device structures, reducing the threading dislocation density in AlN layers on sapphire substrates by high temperature epitaxy is a key parameter for achieving AlGaN-based light emitters with a high efficiency. Stress control and prevention of relaxation is important for obtaining AlGaN layers with a similar dislocation density as the underlying AlN template. A dislocation density below 5 × 108 cm−2 is sufficient for obtaining an efficiency of radiative recombination of 40 % and higher at moderate excitation levels.

Isolated Ti in Si: Deep level transient spectroscopy, minority carrier transient spectroscopy, and high-resolution Laplace deep level transient spectroscopy studies

Combining deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS, and minority carrier transient spectroscopy studies, we question the identification of the dominant Ti-related defects introducing deep levels (E40, E150, and H180) in n- and p-type Si. The observed results cannot unambiguously support the models previously reported for these defects. The presence of the Poole-Frenkel effect describing the enhancement of the emission rates of E40 as a function of electric field is not consistent with the previous assignment of this defect to the single acceptor, whereas the absence of the enhancement of the emission rate of E150 under different reverse bias applied to the diode does not confirm the previous attribution of this defect to the single donor in n-type Si. The attribution of H180 to the double donor is in good agreement with our results. In contrast, the identical depth profiles obtained for E40 and E150 in bulk of as-grown, hydrogenated and annealed samples cannot be explained by the assignment of these levels to different defects.

Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9× 1020cm−3 and 1 × 1020cm−3, respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 1017cm−3, the nanowires are depleted of charge carriers, whereas they become highly conductive above 1019cm−3.

On the behavior of silicon donor in conductive AlxGa1–xN (0.63 ≤ x ≤ 1)

AlxGa1−xN (0.63≤x≤1) layers grown by hot‐wall metal‐organic chemical vapor deposition were intentionally doped with silicon at the atomic concentration of [Si] ∼ 2 × 1018 cm−3. Efficient silicon incorporation into the AlxGa1−xN layers was obtained for all Al contents, x, whereas the resistivity drastically increases for x &gt; 0.84. Degradation of the structural quality and compensation by residual oxygen and carbon impurity were ruled out as possible explanations for the increased resistivity. Frequency dependent capacitance‐voltage measurements indicate that the Si donor is electrically active. Complementary electron paramagnetic resonance measurements suggest formation of stable Si‐related DX centers and increase in the activation energy of the silicon donor for x &gt; 0.84.

Dynamics of free carriers – neutral impurity related optical transitions in Be and Si δ-doped GaAs/AlAs multiple quantum wells: Fractional-dimensional space approach

The dynamics of impurity-related optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels has been investigated at near liquid helium temperatures. The radiative lifetimes of the free electron-neutral acceptor and the free hole-neutral donor have been identified. The capture cross-sections of the free electrons by neutral Be acceptors were experimentally determined to σ e-Be = 4 × 10 –10 cm, whereas this corresponded to σ h-Si = 2.2 × 10 –8 cm for the free holes by neutral Si donors. The experimentally determined cross-section ratio of σ h-Si /σ e-Be = 55 is close to the estimated 2D value of σ h-D /σ e-A = 64 and remains lower compared to the calculated value for the 3D case of σ h-D /σ e-A = 121.

Defects reduction of Ge epitaxial film in a germanium-on-insulator wafer by annealing in oxygen ambient

A method to remove the misfit dislocations and reduce the threading dislocations density (TDD) in the germanium (Ge) epilayer growth on a silicon (Si) substrate is presented. The Ge epitaxial film is grown directly on the Si (001) donor wafer using a “three-step growth” approach in a reduced pressure chemical vapour deposition. The Ge epilayer is then bonded and transferred to another Si (001) handle wafer to form a germanium-on-insulator (GOI) substrate. The misfit dislocations, which are initially hidden along the Ge/Si interface, are now accessible from the top surface. These misfit dislocations are then removed by annealing the GOI substrate. After the annealing, the TDD of the Ge epilayer can be reduced by at least two orders of magnitude to &amp;lt;5 × 106 cm−2.

Fabrication and characterization of germanium-on-insulator through epitaxy, bonding, and layer transfer

A scalable method to fabricate germanium on insulator (GOI) substrate through epitaxy, bonding, and layer transfer is reported. The germanium (Ge) epitaxial film is grown directly on a silicon (Si) (001) donor wafer using a “three-step growth” approach in a reduced pressure chemical vapour deposition. The Ge epilayer is then bonded and transferred to another Si (001) wafer to form the GOI substrate. The Ge epilayer on GOI substrate has higher tensile strain (from 0.20% to 0.35%) and rougher surface (2.28 times rougher) compared to the Ge epilayer before transferring (i.e., Ge on Si wafer). This is because the misfit dislocations which are initially hidden along the Ge/Si interface are now flipped over and exposed on the top surface. These misfit dislocations can be removed by either chemical mechanical polishing or annealing. As a result, the Ge epilayer with low threading dislocations density level and surface roughness could be realized.

Impurity magneto-optical absorption with the participation of resonance states of D 2 − centers in quantum wells

The dependence of the average binding energy of the resonance g-state of a D2− center on the induction of an external magnetic field in a quantum well with a parabolic confining potential is studied using the zero-range potential method. It has been shown that with an increasing exchange interaction, the character of the dependence of the average binding energy of the resonance g-state of the D2− center on the induction of the external magnetic field changes. It has been assumed that in GaAs/AlGaAs quantum wells alloyed with small Si donors, resonance D2− states can exist under conditions of exchange interaction. It has been found that in spectra of impurity magneto-optical absorption in multiwall quantum structures, exchange interaction manifests itself as oscillations of interference origin.