Low resistance bilayer Nd/Al ohmic contacts on n-type GaN

A bilayer Nd/Al metallization structure has been deposited onto low pressure organometallic vapor phase epitaxy grown n-type GaN ( 1 × 10¹⁸ cm⁻³) by electron-beam evaporation. Ohmic metal contacts were patterned photolithographically for standard transmission line measurement, and then thermally annealed at temperatures ranging from 200 to 350°C and from 500 to 650°C using conventional thermal annealing (CTA) and rapid thermal annealing (RTA), respectively. The lowest values for the specify contact resistivity of 9.8 × 10⁻⁶ Ω−cm² and 8 × 10⁻⁶ Ω−cm² were obtained using Nd/Al metallization with CTA of 250°C for 5 min and RTA of 600°C for 30 s. Examination of the surface morphology using atomic force microscopy as a function of annealing temperature revealed that the surface roughness was strongly influenced by conventional thermal annealing, it was smooth in the temperature range from 550 to 650°C for rapid thermal annealing. Auger electron spectroscopy depth profiling was employed to investigate the metallurgy and interdiffusion of contact formation.     

DEEP LEVEL DEFECTS IN SI-IMPLANTED LEC UNDOPED Si-GaAs

The residual electrically active defects in(4×10~(12)cm~(-2)(30KeV)+5×10~(12)cm~(-2)(130KeV))si-implanted LEC undoped si-GaAs activated by two-step rapid thermal annealing(RTA)LABELED AS 970℃(9S)+750℃(12S)have been investigated with deep level transient spec-troscopy(DLTS).Two electron traps ET_1(E_c-0.53eV,σ_n=2.3×10~(-16)cm~2)and ET_2(E_c-0.81eV,σ_n=9.7×10(-13)cm~2)are detected.Furthermore,the noticeable variations of trap's con-centration and energy level in the forbidden gap with the depth profile of defects induced by ion im-plantation and RTA process have also been observed.The[As_i·V_(As)·As_(Ga)]and[V_(As)·As_i·V_(Ga)·As_(Ga)]are proposed to be the possible atomic configurations of ET_1 and ET_2,respectively to explaintheir RTA behaviors.     

Amorphization and Solid-Phase Epitaxial Growth of C-Cluster Ion-Implanted Si

Amorphization and solid-phase epitaxial growth were studied in C-cluster ion-implanted Si. C₇H₇ ions were implanted at a C-equivalent energy of 10 keV to C doses of 0.1 × 10¹⁵ cm⁻² to 8.0 × 10¹⁵ cm⁻² into (001) Si wafers. Transmission electron microscopy revealed a C amorphizing dose of ~5.0 ×  10¹⁴ cm⁻². Annealing of amorphized specimens to effect solid-phase epitaxial growth resulted in defect-free growth for C doses of 0.5 × 10¹⁵ cm⁻² to 1.0 × 10¹⁵ cm⁻². At higher doses, growth was defective and eventually polycrystalline due to induced in-plane tensile stress from substitutional C incorporation.     

Mechanism of defect formation in low-dose oxygen implanted silicon-on-insulator material

The defects and microstructure of low-dose (<0.7 × 10¹⁸ cm⁻²), oxygen-implanted silicon-on-insulator (SIMOX) material were investigated as a function of implant dose and annealing temperature by plan-view and cross-sectional transmission electron microscopy. The threading-dislocations in low-dose (0.2∼0.3×10¹⁸ cm⁻²), annealed SIMOX originate from unfaulting of long (∼10 μm), shallow (0.3 μm), extrinsic stacking faults generated during the ramping stage of annealing. As dose increases, the defect density is reduced and the structure of the buried oxide layer evolves dramatically. It was found that there is a dose window which gives a lower defect density and a continuous buried oxide with a reduced density of Si islands in the buried oxide.     

Boron implantation and epitaxial regrowth studies of 6H SiC

Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×10¹⁶ cm⁻³ and 2×10¹⁸ cm⁻³. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2×10¹⁶ cm⁻³, with a diffusion constant estimated to 1.3×10⁻¹² cm²s⁻¹. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.     

Rapid thermal annealing of si implanted gaas

Rapid thermal annealing (RTA) technology offers potential advantages for GaAs MESFET device technology such as reducing dopant diffusion and minimizing the redistribution of background impurities. LEC semi-insulating GaAs substrates were implanted with Si at energies from 100 to 400 keV to doses from 1 × 10¹² to 1 × 10¹⁴/cm². The wafers were encapsulated with Si₃N₄ and then annealed at temperatures from 850-1000° C in a commercial RTA system. Wafers were also annealed using a conventional furnace cycle at 850° C to provide a comparison with the RTA wafers. These implanted layers were evaluated using capacitance-voltage and Hall effect measurements. In addition, FET’s were fabricated using selective implants that were annealed with either RTA or furnace cycles. The effects of anneal temperature and anneal time were determined. For a dose of 4 × 10¹²/cm² at 150 keV with anneal times of 5 seconds at 850, 900, 950 and 1000° C the activation steadily increased in the peak of the implant with overlapping profiles in the tail of the profiles, showing that no significant diffusion occurs. In addition, the same activation could be obtained by adjusting the anneal times. A plot of the equivalent anneal times versus 1/T gives an activation energy of 2.3 eV. At a higher dose of 3 × 10¹³ an activation energy of 1.7 eV was obtained. For a dose of 4 × 10¹² at 150 keV both the RTA and furnace annealing give similar activations with mobilities between 4700 and 5000 cm²/V-s. Mobilities decrease to 4000 at a dose of 1 × 10¹³ and to 2500 cm²/V-s at 1 × 10¹⁴/cm². At doses above 1 × 10¹³ the RTA cycles gave better activation than furnace annealed wafers. The MESFET parameters for both RTA and furnace annealed wafers were nearly identical. The average gain and noise figure at 8 GHz were 7.5 and 2.0, respectively, for packaged die from either RTA or furnace annealed materials.     

A study on the key factors affecting the electronic properties of monocrystalline silicon solar cells

The model of monocrystalline silicon solar cells is established,and the effects of wafer parameters,such as the p-Si（100） substrate thickness,the defect density,and the doping concentration,on the electronic properties of monocrystalline silicon solar cells are analyzed.The results indicate that the solar cells with an Al back-surface-field will have good electronic properties when the wafers meet the following three conditions：（i） the defect density is less than 1.0×1011 cm^-3;（ii） the doping concentration is from 5×10^15 cm^-3 to 1×10^17 cm^-3,i.e.the bulk resistivity is from 0.5 Ω·cm to 10 Ω·cm;（iii） the cells substrate thickness is in the range of 100 μm to 200 μm.     

Acid etching for accurate determination of dislocation density in GaN

Hot phosphoric-acid etching and atomic force microscopy (AFM) were used to etch and characterize various GaN materials, including freestanding GaN grown by hydride vapor-phase epitaxy (HVPE), metal-organic chemical-vapor deposition (MOCVD) GaN films on sapphire and silicon carbide, and homoepitaxial GaN films on polished freestanding-GaN wafers. It was found that etching at optimal conditions can accurately reveal the dislocations in GaN; however, the optimal etch conditions were different for samples grown by different techniques. The as-grown HVPE samples were most easily etched, while the MOCVD homoepitaxial films were most difficult to etch. Etch-pit density (EPD) ranging from 4×10⁶ cm⁻² to 5×10⁹ cm⁻² was measured in close agreement with the respective dislocation density determined from transmission electron microscopy (TEM).     

Structural and electrical properties of unintentionally doped 4H-SiC epitaxial layers—Grown by hot-wall CVD

This paper focuses on growth of 4H−SiC epitaxial layers using the hot-wall CVD technique. The relation between the growth regime like total flow, system pressure, C/Si ratio and growth temperature and the characteristics of nominally undoped epilayers, such as thickness uniformity and background doping concentration have been investigated. The epitaxial layers were investigated by optical microscopy, capacitance-voltage measurements, x-ray rocking curve maps, electron channelling patterns and secondary ion mass spectroscopy. Layers up to 40 μm in thickness with a variation of about ±4% and with residual n-type doping levels in the low 10¹⁴ cm⁻³ ranges have been obtained on Si faces wafers. SIMS measurements have shown that the impurity concentration of acceptors like B and Al is below 2×10¹⁴ cm⁻³.     

A silicon carbide LOCOS process using enhanced thermal oxidation by argon implantation

A process is described for creating local oxidation of silicon structure (LOCOS) structures in silicon carbide using enhanced thermal oxidation by argon implantation. Thicker oxides were created in selective regions by using multiple energy argon implants at a dose of 1 × 10¹⁵ cm⁻² prior to thermal oxidation. Atomic force microscopy was used to analyze the fabricated LOCOS structure.     

Electronic properties and deep traps in electron-irradiated <Emphasis Type="Italic">n</Emphasis>-GaN

The study is concerned with the effect of electron irradiation (with the energies E = 7 and 10 MeV and doses D = 10¹⁶−10¹⁸ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and the spectrum of deep traps of undoped (concentration of electrons n = 1 × 10¹⁴−1 × 10¹⁶ cm⁻³), moderately Si-doped (n = (1.2−2) × 10¹⁷ cm⁻³), and heavily Si-doped (n = (2−3.5) × 10¹⁸ cm⁻³) epitaxial n-GaN layers grown on Al₂O₃ substrates by metal-organic chemical vapor deposition. It is found that, on electron irradiation, the resistivity of n-GaN increases, this is due to a shift of the Fermi level to the limiting position close to E _c −0.91 eV. The spectrum of deep traps is studied for the initial and electron-irradiated n-GaN. It is shown that the initial properties of the irradiated material are restored in the temperature range 100–1000°C, with the main stage of the annealing of radiation defects at about 400°C.     

Defects in annealed 1.5 MeV boron implanted p-type silicon

Effects of temperature and dosage on the evolution of extended defects during annealing of MeV ion-implanted Czochralski (CZ) p-type (001) silicon have been studied using transmission electron microcopy. Excess interstitials generated in a 1 10¹⁵ cm⁻²/1.5 MeV B⁺ implanted Si have been found to transform into extended interstitial {311} defects upon rapid thermal annealing at 800°C for 15 sec. During prolonged furnace annealing at 960°C for 1 h, some of the {311} defects grow longer at the expense of the smaller ones, and the average width of the defects seems to decrease at the same time. Formation of stable dislocation loops appears to occur only above a certain threshold annealing temperature (∼1000°C). The leakage current in diodes fabricated on 1.5 MeV B⁺ implanted wafers was found to be higher for a dosage of 1 10¹⁴cm⁻² and less, as compared to those fabricated with a dosage of 5 10¹⁴ cm⁻² and more. The difference in the observed leakage current has been attributed to the presence of dislocations in the active device region of the wafers that were implanted with the lower dosage.     

Ga2O3 films formed by electrochemical oxidation

The effect of oxygen plasma on gallium oxide films formed by electrochemical oxidation of n-GaAs wafers with a donor concentration N _d = (1–2) × 10¹⁶ cm⁻³ has been investigated. It is shown that the treatment in an oxygen plasma at a temperature of 50–90°C increases the concentration of β-phase crystallites, which causes an increase in the permittivity, a decrease in the dielectric dissipation factor, and a change in the conductivity of GaAs-〈gallium oxide〉-metal structures.     

Influence of intrinsic point defects on the formation of structural defects and optically active centers during the annealing of erbium-and dysprosium-implanted silicon

The photoluminescence spectra and behavior of the structural defects in layers obtained by implanting 1.0–1.8-MeV Er and Dy ions at a dose of 1×10¹³ cm⁻² are investigated after annealing at 1000–1200 °C for 0.5–1 h in argon or a chlorine-containing atmosphere. The structural defects are studied using transmission electron microscopy and selective chemical etching. The dominant features in the luminescence spectra of the Si:Er and Si:Dy layers following annealing in the chlorine-containing atmosphere are lines associated with the formation of edge dislocations, while the dominant features following the annealing of Si:Er and Si:Dy layers in argon are the erbium-related lines. A comparative analysis of the luminescence spectra of the Si:Er and Si:Dy layers shows that the highest intensity of dislocation-related luminescence is achieved in the erbium-implanted structures. A significant influence of intrinsic point defects on the structural and optical properties of erbium-and dysprosium-implanted silicon is revealed. Fiz. Tekh. Poluprovodn. 33, 656–659 (June 1999)     

Fluorine behavior in BF 2 + implanted polysilicon films subjected to rapid thermal annealing

The physical and electrical properties of BF ₂ ⁺ implanted polysilicon films subjected to rapid thermal annealing (RTA) are presented. It is found that the out diffusion ofF and its segregation at polysilicon/silicon oxide interface during RTA are the major causes ofF anomalous migration. Fluorine bubbles were observed in BF ₂ ⁺ implanted samples at doses of 1×10¹⁵ and 5×10¹⁵ cm⁻² after RTA.     

Heavily Aluminum-Doped Epitaxial Layers for Ohmic Contact Formation to <Emphasis Type="Italic">p</Emphasis>-Type 4H-SiC Produced by Low-Temperature Homoepitaxial Growth

In this work, heavily aluminum (Al)-doped layers for ohmic contact formation to p-type SiC were produced by utilizing the high efficiency of Al incorporation during the epitaxial growth at low temperature, previously demonstrated by the authors’ group. The low-temperature halo-carbon epitaxial growth technique with in situ trimethylaluminum (TMA) doping was used. Nearly featureless epilayer morphology with an Al atomic concentration exceeding 3 × 10²⁰ cm⁻³ was obtained after growth at 1300°C with a growth rate of 1.5 μm/h. Nickel transfer length method (TLM) contacts with a thin adhesion layer of titanium (Ti) were formed. Even prior to contact annealing, the as-deposited metal contacts were almost completely ohmic, with a specific contact resistance of 2 × 10⁻² Ω cm². The specific contact resistance was reduced to 6 × 10⁻⁵ Ω cm² by employing a conventional rapid thermal anneal (RTA) at 750°C. Resistivity of the epitaxial layers better than 0.01 Ω cm was measured for an Al atomic concentration of 2.7 × 10²⁰ cm⁻³.     

Two Layer Surface Exfoliation on Si3N4/Si by Sequential Implantation of He and H Ions

n-Type Si(100) wafers with a thermally grown Si₃N₄ layer (∼170 nm) were sequentially implanted with 160 keV He ions at a dose of 5 × 10¹⁶ cm⁻² and 110 keV H ions at a dose of 1 × 10¹⁶ cm⁻². Depending on the annealing temperature, surface exfoliations of two layers were observed by optical microscopy and atomic force microscopy. The first layer exfoliation was found to correspond to the top Si₃N₄ layer, which was produced at lower annealing temperatures. The other was ascribed to the implanted Si layer, which was formed at higher temperatures. The possible exfoliation processes are tentatively discussed, and potential applications of such phenomena are also suggested.     

Activation efficiencies for a standard qualification implant in gaas annealed by a rapid thermal process

Recently a 150 keV, 2 × 10¹² cm⁻², Si²⁹ implant, with furnace annealing at 850° C for 10 min with a GaAs proximity wafer, has been proposed as a standard qualification test for semi-insulating GaAs. In general, the electrical activation efficiency of implanted wafers is determined either from Hall effect data or from capacitance-voltage (C-V) data; however, the Hall effect method requires sizable depletion corrections at low implant doses. In this paper, we examine the proposed standard, and the methods of determining activation, from three points of view: (1) rapid-thermal annealing (RTA) vs furnace annealing; (2) a Si proximity cap vs a GaAs proximity cap; and (3) Hall effect vs C-V. Our conclusions are: (1) RTA produces higher activation efficiencies, at least for our particular wafers, than furnace annealing; (2) Si and GaAs proximity caps produce nearly equivalent activation efficiencies; and (3) the Hall effect, when corrected for depletion, is a useful technique for measuring activation efficiency, and appears to be more accurate than the C-V technique.     

Nickel Ohmic Contacts to N-Implanted (0001) 4H-SiC

Samples for transmission line model (TLM) and Hall measurements were fabricated on (0001) 4H-SiC implanted with nitrogen at 1 × 10¹⁸ cm⁻³, 4 × 10¹⁸ cm⁻³, 1 × 10¹⁹ cm⁻³, 4 × 10¹⁹ cm⁻³, and 1 × 10²⁰ cm⁻³. Following high-temperature activation, the activation percentage dropped from ~90% to ~20%, and the Hall mobility decreased from ~100 cm²/V · s to ~20 cm²/V · s as the implant concentration increased from 1 × 10¹⁸ cm⁻³ to 1 × 10²⁰ cm⁻³. The specific contact resistance as a function of Hall concentration is compared with published data for Ni contacts to epitaxial layers. The specific contact resistance as a function of activation temperature was also studied for two fixed implant concentrations of 5 × 10¹⁸ cm⁻³ and 1 × 10²⁰ cm⁻³.     

Characterization of Hg0.7Cd0.3Te n- on p-type structures obtained by reactive ion etching induced p- to n conversion

This paper presents transport measurements on both vacancy doped and gold doped Hg_0.7Cd_0.3Te p-type epilayers grown by liquid phase epitaxy (LPE), with N_A=2×10¹⁶ cm⁻³, in which a thin 2 μm surface layer has been converted to n-type by a short reactive ion etching (RIE) process. Hall and resistivity measurements were performed on the n-on-p structures in van der Pauw configuration for the temperature range from 30 K to 400 K and magnetic field range up to 12 T. The experimental Hall coefficient and resistivity data has been analyzed using the quantitative mobility spectrum analysis procedure to extract the transport properties of each individual carrier contributing to the total conduction process. In both samples three distinct carrier species have been identified. For 77 K, the individual carrier species exhibited the following properties for the vacancy and Au-doped samples, respectively, holes associated with the unconverted p-type epilayer with p ≈ 2 × 10¹⁶ cm⁻³, μ ≈ 350 cm²V⁻¹s⁻¹, and p ≈ 6 × 10¹⁵ cm⁻³, μ ≈ 400 cm²V⁻¹s⁻¹; bulk electrons associated with the RIE converted region with n ≈ 3 × 10¹⁵cm⁻³, μ ≈ 4 × 10⁴ cm²V⁻¹s⁻¹, and n ≈ 1.5 × 10¹⁵ cm⁻³, μ ≈ 6 × 10⁴ cm²V⁻¹s⁻¹; and surface electrons (2D concentration) n ≈ 9 × 10¹² cm⁻² and n ≈ 1 × 10¹³ cm⁻², with mobility in the range 1.5 × 10³ cm²V⁻¹s⁻¹ to 1.5 × 10⁴ cm²V⁻¹s⁻¹ in both samples. The high mobility of bulk electrons in the RIE converted n-layer indicates that a diffusion process rather than damage induced conversion is responsible for the p-to-n conversion deep in the bulk. On the other hand, these results indicate that the surface electron mobility is affected by RIE induced damage in a very thin layer at the HgCdTe surface.