A model of reduction of oxidation-enhanced diffusion in heavily doped Si layers

A model of reduction of oxidation-enhanced diffusion (OED) in heavily doped Si layers via bulk recombination of self-interstitials at centers associated with the dopant is suggested. The allowance made for the recombination of excess self-interstitials, which are generated upon thermal oxidation, allows one to describe the dependence of OED reduction on the doping level. The experimental data on the OED of B and P impurities in uniformly doped Si layers are analyzed. From the analysis, the recombination-rate constants are determined and capture radii are estimated for various variants of interaction of excess self-interstitials with impurity atoms and impurity-vacancy pairs.     

Effect of carrier gas and doping profile on the surface morphology of MOVPE grown heavily doped GaN:Mg layers

Semiconductors - Magnesium is the only acceptor impurity practically used in MOCVD of GaN. High activation energy requires high impurity concentration, which results in epilayer morphology...     

Investigation of MOVPE-grown GaN layers doped with As atoms

Conditions are investigated for the injection of arsenic into gallium nitride layers grown by metal-organic vapor-phase epitaxy. It is shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer. The high-temperature overgrowth of a thin GaAs layer by a GaN layer causes As atoms to diffuse into the GaN, produces a thick, homogeneously doped GaN:As region, and creates a bright band in the photoluminescence spectrum with a maximum at ∼2.5 eV. Fiz. Tekh. Poluprovodn. 33, 791–794 (July 1999)     

Formation of heavily doped n-type layers in GaAs by multiple ion implantation

N-type layers in GaAs with high free electron concentrations have been produced by multiple implantation of Ga, As, or P with dopant species such as Se, Si, or Ge. The implants that have been investigated include Si, Si + P, Ge, Ge + As, Se, and Se + Ga. The multiple implants Si + P, Ge + As, and Se + Ga gave higher peak carrier concentrations, especially at lower anneal temperatures, than did the respective single implants Si, Ge, and Se. In fact, Ge when implanted alone produced a p-type layer while the Ge + As multiple implant produced an n-type layer. Multiple implants with Si and Ge as dopants showed significant thermal diffusion during the anneal. Multiple implants of Ga with Se, on the other hand, resulted in reduced thermal diffusion in comparison with single Se implants.     

Growth of n-Si layers by molecular-beam epitaxy on the substrates heavily doped with boron

Epitaxial n-Si layers doped with phosphorus or erbium have been grown by sublimation molecularbeam epitaxy at 500°C on heavily boron-doped p ⁺-type substrates with resistivity ρ = 0.005 Ω cm. Distribution profiles of the B, Er, and O impurity concentrations in the samples were determined by secondary-ion mass spectrometry. A thermal annealing of the substrate in vacuum at 1300°C for 10 min and growth at a very low substrate temperature made it possible to obtain an extremely abrupt profile for doping impurities at the layer-substrate interface. This method for growth of n-p ⁺ junctions considerably improves their electrical and luminescent characteristics.     

未掺杂GaN外延膜的结晶特性与蓝带发光关系的研究

采用卢瑟福背散射／沟道技术，X射线双晶衍射技术和光致发光技术对几个以MOCVD技术生长的蓝带发光差异明显的未掺杂GaN外延膜和GaN：Mg外延膜进行了测试。结果表明，未掺杂GaN薄膜中出现的2．9eV左右的蓝带发光与薄膜的结晶品质密切相关。随未掺杂GaN的蓝带强度与带边强度之比增大，GaN的卢瑟福背散射／沟道谱最低产额增大，X射线双晶衍射峰半高宽增大。未掺杂GaN薄膜的蓝带发光与薄膜中的某种本征缺陷有关。研究还表明，未掺杂GaN中出现的蓝带与GaN：Mg外延膜中出现的2．9eV左右的发光峰的发光机理不同。     

Effect of uniform compression on photoluminescence spectra of GaAs layers heavily doped with beryllium

The effect of high-temperature annealing at high hydrostatic pressures on photoluminescence of heavily doped GaAs:Be layers grown by molecular-beam epitaxy on GaAs substrates was studied. A blue shift of the band-edge luminescence line and an increase in the relative intensity of the shoulder at the high-energy wing of this line were detected after annealing in the spectra of layers with a beryllium atom concentration higher than 5×10¹⁹ cm^?3. The same layers featured a concentration-related decrease in the GaAs lattice parameter, which does not conform to the Vegard law. These effects can be attributed to the formation of beryllium inclusions in heavily doped GaAs. Due to different compressibility and thermal expansion coefficients of Be inclusions and GaAs, high-temperature and high-pressure treatment gives rise to structural defects; hence, the probability of transitions that are indirect in the k space increases.     

Specific features of the segregation-related redistribution of phosphorus during thermal oxidation of heavily doped silicon layers

A model of the diffusion-segregation redistribution of phosphorus in an SiO₂/Si system during thermal oxidation of highly doped silicon layers is developed taking into account the formation of a peak of surface impurity concentration at the interface. The formation of this surface concentration peak is attributed to a change in the free energy of the impurity atoms near the silicon surface. This process is simulated by a diffusion-segregation equation. It is shown that the developed diffusion-segregation model is quite adequate for describing the phosphorus redistribution occurring during the oxidation of uniformly doped silicon layers. For the oxidation of implanted silicon layers, it was found that the segregation coefficient of the phosphorus at the SiO₂/Si interface is not constant but depends on time in the same way as the efficiency of transient enhanced diffusion in silicon. This phenomenon is explained by the reactivity of the impurity segregation during the thermal oxidation of silicon, when excess point defects in the implanted silicon layer affect both the oxidation process and the capture of impurity atoms by the growing silicon dioxide.     

Thermal stability of Ni silicide films on heavily doped n and p Si substrates

Electrical and structural properties of Ni silicide films formed at various temperatures ranged from 200 °C to 950 °C on both heavily doped n⁺ and p⁺ Si substrates were studied. It was found that surface morphology as well as the sheet resistance properties of the Ni silicide films formed on n⁺ and p⁺ Si substrates at the temperatures higher than 600 °C were very different. Agglomerations of Ni silicide films on n⁺ Si substrates begin to occur at around 600 °C while there is no agglomeration observed in Ni silicide films on p⁺ Si substrates up to a forming temperature of 700 °C. It was also found that the phase transition temperature from NiSi phase to NiSi₂ phase depend on substrate types; 900 °C for NiSi film on n⁺ Si substrate and 750 °C for NiSi film on p⁺ Si substrate, respectively. Our results show that the agglomeration is, especially, important factor in the process temperature dependency of the sheet resistance of Ni silicides formed on n⁺ Si substrates.     

Dependence of the concentration of ionized donors on epitaxy temperature for Si:Er/Si layers grown by sublimation molecular-beam epitaxy

The dependence of the concentrations of the Er impurity and ionized donors on the epitaxy temperature has been studied before and after annealing of Si:Er/Si layers grown by sublimation molecular-beam epitaxy. n-Si:Er layers have been grown in the temperature range 400–800°C and annealed in hydrogen atmosphere at a temperature of 800°C for 30 min. The possible nature of the donor centers is discussed.     

Optical characterization of heavily doped silicon

Out of a variety of optical techniques used to characterize heavily doped semiconductors photoluminescence and Raman spectroscopy will be discussed as tools to study heavy doping effects. Photoluminescence spectroscopy is sensitive to electronic transitions between the conduction and valence band whereas electronic Raman scattering probes transitions within either band. Parameters relevant to device physics such as the band gap shrinkage due to heavy doping are extracted from these measurements. It is further shown that both techniques are applicable to the characterization of thin heavily doped implanted or epitaxial layers.     

Temperature-dependent resistive switching characteristics for Au/n-type CuAlOx/heavily doped p-type Si devices

Bipolar switching phenomenon is found for Au/n-type CuAlO_x/heavily doped p-type Si devices at temperatures above 220 K. For high or low resistive states (HRS or LRS), the electrical resistance is decreased with increasing temperature, indicating a semiconducting behavior. Carrier transport at LRS or HRS is dominated by hopping conduction. It is reasonable to conclude that the transition from HRS to LRS due to the migration of oxygen vacancies (V_O) is associated with electron hopping mediated through the V_O trap sites. The disappearance of the resistive switching behavior below 220 K is attributed to the immobile V_O traps. The deep understanding of conduction mechanism could help to control the device performance.     

Magnetic ordering effects in heavily doped GaAs:Fe crystals

The exchange coupling of Fe centers in GaAs crystals is studied by electron spin resonance (ESR). Transitions to a superparamagnetic state and to an impurity ferromagnetism domain are analyzed. A study of a system of single-domain magnetically ordered regions in GaAs:Fe with the transition to a ferromagnetic state occurring at the temperature T_C1 = 460 K is described. It is shown that impurity ferromagnetism with a transition temperature T_C2 of 60 K in a disordered system of Fe centers randomly distributed among superparamagnetic regions exists in GaAs:Fe.     

The study on the radial distribution of delta [Oi] in heavily doped Si wafer using X-ray diffraction

The radial distribution of the delta [Oi] for the heavily doped silicon wafers was investigated using X-ray diffraction technique. In order to obtain the correlation between delta [Oi] and X-ray intensity ratio for the lightly doped wafers with different initial [Oi] concentrations, the oxygen concentration using FTIR and X-ray intensity were measured before and after two-step annealing. The relation between delta [Oi] and X-ray intensity ratio showed that it was close to the parabolic correlation rather than the linear correlation. The deviation of this measurement was about ±0.4 ppma. This correlation equation could be applied to the heavily doped wafers. It is shown that the radial distribution of the delta [Oi] is not uniform in the radial direction but has the symmetric relation at the wafer center. The bulk micro defect (BMD) density using etching method was measured to confirm these results.     

Leakage mechanisms in the heavily doped gated diode structures

A leakage current model is presented which shows very good agreement with reported experimental results on gated diode structures with contemporary ULSI dimensions. The leakage current is modeled as the Shockley-Read-Hall generation current, enhanced by the Poole-Frenkel effect and trap-assisted tunneling. The model shows very good agreement on gate voltage, temperature, and oxide thickness dependence for the normal operating voltage range. It is found from the model that the doping range from 2×10¹⁸ to 1×10¹⁹ cm ^-3 gives the most significant degradation to the leakage characteristics in trench-type DRAM cells and the drain of MOSFETs     

Measurements of the p-n product in heavily doped epitaxial emitters

A new method is described for the measurement of the p-n product in the heavily doped epitaxial emitters of biopolar tansistors. Quantitative electron-beam-induced conductivity is used to determine the diffusion length in the emitter as well as the emitter thickness. I - V characterization and other standard methods are then used to measure the p-n product. The principal advantage of this method is that corrections for recombination in both the emitter and the base can be made based on measurements on identical regions of the same device. A key problem with other methods for determining the p-n product is their inability to separate changes in the p-n product (bandgap narrowing) from recombination, based on measurements taken on the same region of the device. New data for the p-n product at ∼ 10²⁰.cm³free-carrier electron density are uniformly compared to other published data. The importance of the effective bandgap narrowing parameter both for comparing experimental data and for device modeling is stressed. Diffusion length measurements on the more heavily doped emitters yield lifetimes longer than expected based on published lifetimes determined by the decay of optical luminescence in heavily doped silicon. Possible reason for this difference are discussed and attributed to gettering in our samples.     

Measurement of the minority-carrier transport parameters in heavily doped silicon

A new method for simultaneous measurement of bandgap narrowing and diffusion length in a heavily doped n⁺substrate is proposed. The method uses planar test pattern at the front side of the substrate to determine the hole minority-carrier current injected from a p-type emitter and diodes at the rear side to measure diffusion lengths. The method can be generalized such that the minority-carrier diffusion constant can be estimated and the use of extrapolated literature data can be avoided. Results of measured values of bandgap narrowing and diffusion length versus impurity concentration are given for n-type material.     

Electrical properties of heavily doped polycrystallinesilicon-germanium films

The electrical properties of polycrystalline silicon-germanium (poly-Si_1-xGe_x) films with germanium mole fractions up to 0.56 doped by high-dose ion implantation are presented. The resistivity of heavily doped p-type (P⁺) poly-Si_1-x Ge_x is much lower than that of comparably doped poly-Si, because higher levels of boron activation and higher hole mobilities are achieved in poly-Si_1-xGe_x. The resistivity of heavily doped n-type (N⁺) poly-S_1-xGe_x is similar to that of comparably doped poly-Si for x<0.45; however, it is considerably higher for larger Ge mole fractions due to significant reductions in phosphorus activation. Lower temperatures (~500°C), as well as lower implant doses, are sufficient to achieve low resistivities in boron-implanted poly-Si_1-xGe_x films, compared to poly-Si films. The work function of P⁺ poly-Si_1-xGe_x decreases significantly (by up to ~0.4 Volts), whereas the work function of N⁺ poly-Si_1-xGe_x decreases only slightly, as Ge content is increased. Estimates of the energy bandgap of poly-Si_1-xGe_x show a reduction (relative to the bandgap of poly-Si) similar to that observed for unstrained single-crystalline Si_1-xGe_x for a 26% Ge film, and a reduction closer to that observed for strained single-crystalline Si _1-xGe_x for a 56% Ge film. The electrical properties of poly-Si_1-xGe_x make it a potentially favorable alternative to poly-Si for P⁺ gate-material applications in metal-oxide-semiconductor technologies and also for p-channel thin-film transistor applications