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We demonstrated electrical characteristics of operational amplifier (OPAMP) circuits fabricated by GaN/AlGaN/GaN HEMTs operating over 100 oC. GaN/AlGaN/GaN HEMTs, with the extremely low source resistance were fabricated by multiple ion implantation, precisely controlled ion-implanted (I/I) resistors and Schottky barrier diodes were integrated on the silicon substrate. The GaN cap layer on the AlGaN was grown to decrease the gate leakage current and current collapse for AlGaN/GaN HEMTs.
We investigated triple ion implanted 4H-SiC BJT with etched extrinsic base regions. To remove the defects induced by ion implantation between emitter and base regions, the characteristics of triple ion implanted 4H-SiC BJT were significantly improved. Maximum common current gain was improved from 1.7 to 7.5.
Double ion implanted 4H-SiC bipolar junction transistors (BJTs) are fabricated by Al and N ion implantation to the base and emitter. The current gain of 3 is obtained at the base Al concentration of 1 × ∼ 1017 /cm3. The collector current as a function of the base Gummel number suggests that double ion implanted 4H-SiC BJT operates in the intrinsic region below the emitter in the low injection level. The high base resistance restricts the base current at VBE as low as 3 V.
Multiple ion-implanted GaN/AlGaN/GaN high electron-mobility transistors (HEMTs) and preciously controlled ion-implanted resistors integrated on silicon substrate are reported. Using ion implantation into source/drain (S/D) regions, the performances were significantly improved. On-resistance reduced from 10.3 to 3.5 Ω•mm. Saturation drain current and maximum transconductance increased from 390 to 650 mA/mm and from 130 to 230 mS/mm. Measured transfer curve shows that I/O gain of 4.5 can be obtained at Vdd = 10 V.
The sheet resistance and sheet carrier concentration for Si ion implanted GaN have been investigated as a function of Si ion dosages and ion's energy using van der Pauw method and Hall effect measurement. Si ion implanted GaN is annealed at 1200 °C for 10 sec in N2 gas flow with 50 nm-thick SiNx cap layer to avoid dissociation of GaN. For Si ion energy of 30 keV, the sheet resistance is decreased from 103 to 56 ohm/sq. for the dose ranging from 1 × 1014 to 2 × 1015/cm2. For the Si dose larger than 2 × 1015/cm2, the sheet carrier concentration is saturated around 1 ×s 1015/cm2. Si ion implanted GaN with energy of 50, 80, and 120 keV at a dose of 2 × 1015/cm2 also reveal the sheet carrier concentration of about 1 × 1015/cm2 with the decrease of electron mobility. It is suggested that the implanted Si donors are strongly compensated by the residual implantation-induced defects.
In this paper, we demonstrate that high temperature and short time EBAS annealing is effective to obtain low sheet resistance without surface roughening in heavily Al-implanted 4H-SiC (0001) samples (Al concentration: 1.0 × 1021 /cm3, thickness: 0.3 microns, total dose: 2.6 × 1016 /cm2). The sheet resistance and rms surface roughness of the sample annealed at 1800 °C for 0.5 min is estimated to be 4.8k ohm/sq. and 0.82 nm, respectively. Also, we discuss the advantage of EBAS annealing for the suppression of surface roughening during annealing.
We demonstrate the realization of compatibility of extremely low gate leakage current and low source resistance with Si ion-implanted (I/I) GaN/AlGaN/GaN surface-stabilized high-electron mobility transistor (HEMT) without any recess etching process. The source/drain regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into source/drain (S/D) regions with energy of 80 keV, the performances were significantly improved. On-resistance (Ron) reduced from 105 to 9.2 Ω·mm. Saturation drain current (Idss) and maximum transconductance (gmMAX) increased from 49 to 527 mA/mm and from 13 to 84 mS/mm (Vg=+1V).
Incorporation of Si ion implantation to GaN metal semiconductor field effect transistor (MESFET) processing has been demonstrated. The channel and source/drain regions formed using Si ion implantation into undoped GaN on sapphire substrate. In comparison with the conventional devices without ion implanted source/drain structures, the ion implanted devices showed excellent device performance. On-state resistance reduces from 210 Ω-mm to 105 Ω-mm. Saturation drain current and maximum transconductance increase from 36 mA/mm to 78 mA/mm and from 3.8 mS/mm to 10 mS/mm, respectively.
Ti/Al ohmic contact with an extremely low specific contact resistance has been formed by the deposition of Ti and Al films on Si+ lanted GaN. The ohmic contact formed by annealing at 600 o C of Ti film with a thickness of 50 nm and Al film with a thickness of 200 nm reveals the good smooth surface and uniform structure as compare to those of contacts formed above 700 °C, which is correlated to whether the Al-Ti alloy is melted during the annealing of ohmic contact or not. The specific contact resistance of 2 × 10-6Ω-cm2 is obtained for Si+ implanted GaN with a dose of 5 × 1013 cm-2. As Si ion dose increases to 5 × 1014 /cm2, the specific contact resistance is reduced to 2 × 10-8 Ω-cm2. It is revealed that the selective doping at high impurity concentration in the surface region by Si+ implantation is useful to reduce the contact resistance for Ti/Al contact to GaN.
With the aim of lowering epitaxial growth temperature, the effect of electron incidence is studied in the epitaxial growth of CeO2(110) layers on Si(100) substrates by electron-beam evaporation in an ultrahigh vacuum. Two growth methods are employed: evaporation under substrate bias application and electron-beam assisted evaporation. In evaporation at positive substrate bias, electrons and anions from an evaporation source are attracted to the substrate surface, resulting in successful epitaxial temperature lowering. It is clarified that facilitation of the epitaxial growth is attributed only to electron incidence. The electronic current component is measured to be on the order of 10−4 A, about half of the total current. In using electron-beam assisted evaporation for higher current (10−3 A), electron-beam irradiation is demonstrated to have a much greater effect in both the growth temperature lowering and the crystalline quality improvement. The epitaxial growth facilitation effect increases with electron energy in both evaporation methods. It is clarified that the epitaxial growth temperature is lowered to 720°C, i. e., epitaxial growth temperature lowering of ∼100°C compared with the conventional growth method, both by evaporation with substrate bias at +240 V and 240 eV-electron-beam assisted evaporation, wherein the latter produces higher crystalline quality layers.
Epitaxial growth of CeO2 layers on silicon (100) substrates is studied using electron-beam evaporation under substrate bias application in an ultrahigh vacuum. Both negative and positive biases are proved to be effective for lowering the epitaxial temperature. Sample current characteristics are measured as a function of the bias voltage. Under negative bias conditions, as the bias voltage increases, the sample current varies from negative to positive with a transition point at -42 V and then reaches a saturation value of ∼ +4 μA above -60 V. Use of a negative bias of -60 V leads to epitaxial growth temperature lowering of ∼, 40°C. Under a positive bias, the sample current is negative and its absolute value increases with the bias voltage, where the sample current components are to be anions and electrons (46°) as determined by mass separation with a magnetic field application. It is experimentally clarified that the degree of enhancement of epitaxial growth is greater than that in the negative bias experiment (750°C at +60 V bias, i. e., epitaxial growth temperature lowering of 70°C) and the enhancement is attributed to the electron component. It is found that a negative current of ∼ -0.15 mA flows at zero bias, indicating that even in conventional evaporation, electrons somewhat promote epitaxial growth.
The substrate off-orientation effect is systematically studied on epitaxial CeO2(110) layers on Si(100), and the crystalline quality is significantly improved by enhancement of domains whose 〈110〉 is perpendicular to the offset-direction (Si〈110〉). AFM measurements indicate that the CeO2 layer surface consists of stripe-shaped facets and that their size is typically 100˜200 nm long, 20 nm wide and ∼3 nm high for a 150 nm-thick layer. RHEED and XTEM reveal that CeO2〈110〉 axis is inclined from wafer normal by the off-angle. The step arrangement at Si surface observed by XTEM relates closely to the inclination of the facets. It is found that off-orientation (≥∼,2.5°) leads to single crystal layer formation. RBS analyses verify that the crystalline quality is significantly improved, especially at the surface. The best result is obtained at the off-angle of 2.5°.
Surface morphology evolution of epitaxially grown CeO2(110) layers on Si(100) substrates is studied using atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED). The surface has a faceted structure; a stripe-appearance and triangular-shape in plan- and cross-sectional views, respectively. AFM measurements clarify that as the layer thickness increases, the cross-sectional shape changes from a gable roof shape toward trapezoidal, which is consistent with RHEED analyses. The width of the facet monotonically increases with the layer thickness, while its height saturates at ∼5 nm above 600 nm in thickness, which means that the surface approaches smooth morphology. Ion channeling analyses indicate that the thicker the layer, the better the crystalline quality at the surface.
Epitaxially grown CeO2 layers on (100)Si substrates are studied using the RBS/channeling technique. The crystallographic correlation between the overgrown layers and off-oriented Si substrates is precisely analyzed by means of constructing stereographic projections obtained from the planar channeling dips. From the stereographic projections for the CeO2 layer on the 4° off-oriented Si substrate, it is clearly seen not only that the epitaxial (110)CeO2 layer is single crystal with the direction defined as CeO2 ║ Si, but also that the crystalline quality of (110)CeO2 on (100)Si can be improved by use of the off-oriented substrate. The inclined epitaxial direction is also detected as the depth information.
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