闭管扩散Zn对InP表面性质的影响

利用闭管扩散方法以Zn3P2为扩散源，在不同扩散温度和扩散时间下对非故意掺杂InP (100）晶片进行扩散. 用电化学C-V法（ECV）和二次离子质谱法(SIMS)分别测出了空穴浓度和Zn的浓度随深度的分布曲线. 结果表明扩散后InP表面空穴和Zn的浓度在扩散结附近突然下降，InP表面空穴浓度主要取决于扩散温度，扩散深度随着扩散时间的增长而变大，InP表面Zn浓度一般比空穴浓度高一个数量级. 另外对扩散后的样品进行光致发光（PL) 测试，表明在保证表面载流子浓度的同时，适当降低扩散温度和增加扩散时间能减小对InP表面性质的影响.     

Experimental investigation of the excess charge

The open-circuit voltage of about 600 mV developed by 0.1 ohm-cm silicon solar cells under air mass zero illumination is about 100 mV less than voltages predicted from simple diffusion theory. The lower measured voltages appear to be controlled by junction current transport processes associated with the thin top diffused layer. Mechanisms such as low n⁺ layer minority carrier lifetime and bandgap narrowing due to heavy doping effects (HDE) have been suggested to explain these results. Experimental determinations of the properties of the diffused layer are required to assess which of these mechanisms predominate. While direct measurement is difficult, an indirect measurement methodology exists by which the lifetime or transit time in the diffused layer can be obtained. Nine p-type, 1×2 cm, 〈111〉 orientation silicon wafers were phosphorus diffused at 880°C for 45 minutes using P0Cl₃. Open-circuit voltages of 595-612 mV, typical of all 0.1 ohm-cm cell voltages, were obtained. From the open-circuit voltage and short-circuit current, the diffusion controlled I₀ was obtained. In addition to illuminated I-V characteristics, the time constants from the Open-Circuit Voltage Decay method, and the minority carrier diffusion lengths in the base region were measured. The base region charge was determined using the base region diffusion length measured by an X-ray method. The data from these experiments combined with simple theory can imply the minority carrier time constant and the excess charge in the diffused layer. From this, certain conclusions are drawn about the relative roles of bandgap shrinkage and recombination rates in the diffused layer.     

Modeling and measurement of minority-carrier lifetime versus doping in diffused layers of n+-p silicon diodes

The results of minority-carrier lifetime measurements in heavily phosphorus-doped n⁺diffused layers of p-n junction diodes using a spectral response technique are reported in this paper. Exact modeling of current-flow equations, modified to include bandgap reduction due to high carrier concentration and Auger recombination, is used to compute the dependence of diffused-layer photocurrent Jpthon the incident light energy and intensity. The photocurrent in the diffused layer is also obtained by subtracting the theoretical value of the space charge and uniformly doped p-region component from the experimentally measured photocurrent of the diode at each wavelength. Note that all calculated values based on light intensity include computed transmittance/reflectance through the oxide layer at each wavelength. The comparison of the values of Jpthwith Jpexp, using nonlinear least square techniques, then directly gives the lifetime profile in the diffused layer. A simple expression is given for lifetime as a function of doping which may be used in modeling and prediction of device performance. Using this experimental technique it was found that the lifetime in the diffused layer is an order of magnitude less than that corresponding to uniformly doped bulk-silicon values and is very much process dependent; its value being 3.72 × 10^-11s for surface concentration of 3.0 × 10²⁰cm^-3and increases to 2.9 × 10^-8s at doping concentration of 1.0 × 10¹⁷cm^-3.     

Sodium Effects on the Diffusion,Phase, and Defect Characteristics of Kesterite Solar Cells and Flexible Cu2ZnSn(S,Se)4 with Greater than 11% Efficiency

Improving the efficiency of kesterite (Cu₂ZnSn(S,Se)₄; CZTSSe) solar cells requires understanding the effects of Na doping. This paper investigates these effects by applying a NaF layer at various positions within precursors. The NaF position is important because Na produces Na-related defects in the absorber and suppresses the formation of intrinsic defects. By investigating precursors with various NaF positions, the sulfo-selenization mechanism and the characteristics of defect formation are confirmed. Applying a NaF layer onto a Zn layer in a CZTSSe precursor limits Zn diffusion and suppresses Cu-Zn alloy formation, thus changing the sulfo-selenization mechanism. In addition, the surface NaF layer provides reactive Se and S to the absorber layer by generating Na₂Se_x and Na₂S_x liquid phases during sulfo-selenization, thus limiting the incorporation of Na into the absorber and reducing the Na effects. Efficiency values of 11.16% and 11.19% are obtained for a flexible CZTSSe solar cell by applying NaF between the Zn layer and back contact and between the Cu and Sn layers, respectively. This study presents methods for doping with alkali metals and improving the efficiency of photovoltaics.     

Surface morphology of 6H-SiC after thermal diffusion

Diffusion of aluminum into 6H-SiC has been carried out in the temperature range of 1800–2100°C. Aluminum carbide (Al₄C₃) was used for a p-type impurity source; the diffused surface exhibited good stoichiometry and surface morphology. A thin-layer graphite film was developed to protect the wafer surface from deterioration during the high-temperature diffusion process. A high-resolution optical microscope (HROM) and atomic force microscopy (AFM) were employed to evaluate the surface morphology of the diffused samples. The protective graphite layer significantly decreased the surface roughness. X-ray photoelectron spectroscopy (XPS) was used to identify the Si/C ratio near the surface regions. Very little surface graphitization occurred during diffusion. In addition, secondary ion-mass spectroscopy (SIMS) was used to investigate the influence of the thin graphite film on the diffusion properties in SiC. There were no significant differences in doping profiles in the samples with and without the graphite film.     

Effect of surface encapsulation and As4 overpressure on Si diffusion and impurity-induced layer disordering in GaAs,AlxGa1-xAs,and AlxGa1-xAs-GaAs quantum well heterostructures

Data are presented demonstrating that the surface encapsulant and the As₄ overpressure strongly affect Si diffusion in GaAs and Al_xGa_1-xAs, and thus are important parameters in impurity-induced layer disordering. Increasing As₄ overpressure results in anincrease in diffusion depth in the case of GaAs, and adecrease in diffusion depth for Al_xGa_1-xAs. In addition, the band-edge exciton is observed in absorption on an Al_xGa_1-xAs-GaAs superlattice that is diffused with Si and is converted to bulk crystal Al_yGa_1-yAs via impurity-induced layer disordering. In contrast, the exciton is not observed in absorption on GaAs diffused with Si in spite of the high degree of compensation. These data indicate that the Si diffusion process, and the properties of the diffused material, are different for GaAs and for Al_xGa_1-xAs-GaAs superlattices converted into uniform Al_yGa_1-yAs (0 ≤y ≤x ≤ 1) via impurity-induced layer disordering with the amphoteric dopant Si.     

Characteristics of gradually doped LWIR diodes by hydrogenation

The hydrogenation effects on HgCdTe diode performance are presented and the mechanism of hydrogenation is revealed. By the hydrogenation, R₀A is increased by 30 times and photo-response is also improved. It is supposed that these are explained by the increased minority carrier lifetime by the hydrogenation. However, it is found from LBIC measurements that the minority carrier lifetime doesn’t increase by the hydrogenation. An important clue that explains the hydrogenation effects is found from Hall measurements. It is found that, after the hydrogenation, the doping concentration of Hg-vacancy doped substrate decreases and the mobility increases. For the heavily hydrogenated bulk substrate, it is also found that the hydrogen passivates the whole Hg-vacancy and reveals the residual impurity and p-type doping concentration is exponentially graded. From these measurements, the diffusion current model of gradually doped diode is proposed. This model shows that the diffusion current of the graded junction diode is 2 orders of magnitude smaller than that of the abrupt junction diode, which clearly explains the R₀A increase by the hydrogenation. Medicisimulation to investigate the change of LBIC signal by the doping grading also coincides with the measurements. From these measurements and model, the hydrogenation effects are attributed to the grading of Hg-vacancy doped p-type substrate by the diffused hydrogen.     

Optical properties of annealed,single GaAs quantum wells: Cap doping and mask width dependence

Band edge absorption measurements are used to characterize the degree of Al-Ga intermixing (blue-shifting) and the linear optical loss of waveguides formed in five annealed and encapsulated single GaAs quantum well laser heterostructure wafers which differed only by the amount of Zn doping in the GaAs cap layer. In addition to the transmission measurements, secondary ion mass spectroscopy data was used to verify the diffusion of Zn before and after annealing. High zinc doping in the cap is observed to cause quantum well disordering below the encapsulant (Si₃N₄) and is attributed to impurity induced layer disordering. Moderate doping in the cap results in selective area intermixing via controlled gallium vacancy production. A stripe width dependence is also observed, which suggests a role of lateral diffusion of species which affect the intermixing. For an undoped (n⁻) cap, the degree of intermixing is heavily dependent on the arsenic overpressure used during the anneal and is independent of the nitride stripe width suggestive of a volumetric Fermi level dependent production of vacancies within the cap.     

Equivalent doping profile transformation: a new analytical method to predict breakdown voltage of the composite pn junction

This paper describes a new analytical method called the equivalent doping profile of a composite p–n junction, that is, a simplified diffused junction with a linear gradient G _L on the diffused side and a constant concentration N _sub on the substrate. The analytical results for various combinations of the substrate doping concentration and the diffused side gradient levels agree well with the numerical analysis, showing the validity of the method presented here.     

Effects of S,Si, or Fe dopants on the diffusion of Zn in InP during MOCVD

Diffusion of Zn in InP during growth of InP epitaxial layers has been investigated in layer structures consisting of Zn-InP epilayers grown on S-InP and Fe-InP substrates, and on undoped InP epilayers. The layers were grown by metalorganic chemical vapour deposition (MOCVD) atT = 625° C andP = 75 Torr. Dopant diffusion profiles were measured by secondary ion mass spectrometry (SIMS). At sufficiently high Zn doping levels ([Zn] ≥8 × 10¹⁷ cm⁻³) diffusion into S-InP substrates took place, with accumulation of Zn in the substrate at a concentration similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels, probably associated with interstitial Zn diffusion. For diffusion into Fe-InP, this low level diffusion produced a region of constant Zn concentration at [Zn] ≈ 3 × 10¹⁶ cm⁻³, due to kick-out of the original Fe species from substitutional sites. We also investigated diffusion out of (Zn, Si) codoped InP epilayers grown on Fe-InP substates. The SIMS profiles were characterised by a sharp decrease in [Zn] at the epilayer-substrate interface; the magnitude of this decrease corresponded to that of the Si donor level in the epilayer. For [Si] ≫ [Zn] in the epilayer no Zn diffusion was observed; Hall measurements indicated that the donor and acceptor species in those samples were electrically active. All these results are consistent with the presence of donor-acceptor interactions in InP, resulting in the formation of ionised donor-acceptor pairs which are immobile, and do not contribute to the diffusion process.     

Barrier height control of Pd2 Si/Si schottky diodes using diffusion from doped Pd

The barrier height of metal-semiconductor contacts can be varied within wide limits by a suitable doping (Sb, Al) of the metal layer itself and application of a temperature treatment to the sandwich structure. As a result the doping elements are weakly diffused into the semiconductor surface. This leads to a change of the band bending and finally to a change of the barrier height. $\text{Pd}{}_2\text{Si}\text{n-}\text{Si}$ diodes with barrier heights q·φ_B between 0.5 and 0.8 eV were fabricated reproducibly by this method. The barrier height of undoped Pd₂Si/Si contacts equals 0.72 eV. The doping elements were introduced into the metal layer by partly covering the Pd-cathode of a DC-sputtering apparatus with Al or Sb, and subsequent sputtering of the composite cathode onto the silicon slices.The concentration of doping elements in the sputtered metal layer is given by the relation of the part of the cathode surface covered with the doping element to the whole cathode surface.     

Zn doping of InP, InAsP/InP, and InAsP/InGaAs heterostructures through metalorganic vapor phase diffusion (MOVPD)

Zinc incorporation by post-growth metalorganic vapor phase diffusion (MOVPD) is used to achieve high p-doping, which is desirable for the fabrication of photodiodes. Diethylzinc (DEZ) is used as precursor and Zn is diffused into InP and InAs_0.6P epitaxial layers grown by low pressure metalorganic vapor phase epitaxy (MOVPE) on different substrate orientations, enabling the investigation of the dislocation density on the Zn incorporation. Diffusion depths are measured using cleave-and-stain techniques, resistivity measurements, electrochemical profiling, and secondary ion mass spectroscopy. High hole concentrations of, respectively, 1.7 10¹⁹ and 6 10¹⁸ cm⁻³, are obtained for, respectively, InAs_0.60P and InP. The diffusion coefficients are derived and the Zn diffusion is used for the fabrication of lattice-mismatched planar PIN InAsP/InGaAs photodiodes.     

Monomolecular layer epitaxy of GaAs for ideal static induction transistor

An ideal static induction transistor (ISIT) structure was fabricated using molecular layer epitaxy (MLE). The doping method of MLE enabled us to achieve a sufficiently high level of doping for ISIT fabrication. In the fabrication process a low growth temperature was very important for the device structure, which requires very sharp dopant profiles. For the ISIT, two MLE processes, namely source–drain growth and gate regrowth, were required. The electrical characteristics of the source–drain were changed after heat treatment at a temperature higher than 480°C. The effect of the redistribution of dopants of the source–drain structure (n⁺⁺–i–p⁺⁺–i–n⁺) during gate regrowth was clearly shown by SIMS (secondary ion mass spectroscopy) measurements for various temperatures of heat treatment. As a result the doped Se diffused from the n⁺⁺ source region to the other layers and the doped Zn diffused from the p⁺⁺ layer to the i-layers. The source was a heavily Se-doped layer at the doping level of (2–3)×10¹⁹ cm⁻³ containing a larger amount of interstitial Se atoms in the lattice. The redistribution of Se from the heavily doped region was detectable even after heat treatment at 480°C for 30 min. For the p⁺⁺ layer the profile of the C-doped layer was stable even after heat treatment at 620°C for 30 min, but the profile of Zn changed markedly after heat treatment at 480°C for 30 min. In addition, the carbon-doped p⁺⁺ layer acted as a gettering layer for diffused interstitial Se from the source region. The driving force of the redistribution of dopants results in the electric field in the device structures. © 1997 John Wiley & Sons, Ltd.     

InP基光电探测器材料的MOCVD锌扩散

锌(Zn)扩散是制作InP基光电探测器(PD)的重要工艺过程.分析了锌扩散的机制,利用金属有机化学气相沉积(MOCVD)设备对InP基PD及雪崩光电探测器(APD)材料进行了锌扩散,由于MOCVD设备具有精确的温度控制系统,所以该扩散工艺具有简单、均匀性好、重复性好的优点.对于扩散后的样品,采用电化学C-V方法和扫描电子显微镜(SEM)等测试分析手段,研究了退火、扩散温度、扩散源体积流量和反应室压力等主要工艺参数对InP材料扩散速率和载流子浓度的影响,并将该锌扩散工艺应用于InP基光电探测器和雪崩光电探测器的器件制作中,得到了优异的器件性能结果.     

Cooperative effects between arsenic and boron in silicon during simultaneous diffusions from ion implanted and chemical source predepositions

Simultaneous diffusions of As and B from predeposited layers (chemical source or ion implantation) have been used in order to fabricate the emitter and base regions, respectively, of microwave transistors. Mathematical simulations of the doping profiles in these transistors have shown that the cooperative diffusion effects that occur in sequentially diffused As-B structures (chemical sources) are noticeably absent in the predeposited-diffused structures. The result is that transistors that are fabricated via this technique show no base retardation, and the active base doping concentrations are higher than predicted by previously established diffusion equations. In order to determine the extent to which cooperative effects are important, transistor doping profiles were measured and compared with calculated profiles. By including the electric field interaction, the vacancy undersaturation condition due to [V_SiAs₂] complex formation, and ion pairing, it was possible to estimate the significance of each effect upon the B diffusion. It is shown that the electric field interaction is two- to three-times smaller in a predeposited-diffused structure than in a constant surface concentration diffusion (non-depleting source). More importantly, a negligible undersaturation of vacancies occurs during simultaneous As-B diffusions from predeposited layers. In the case of a chemical source As predeposition, this is due to the fact that a quasi-equilibrium concentration of [V_SiAs₂] complexes is achieved during the predeposition (before the simultaneous diffusion with B). In the case of an As implantation predeposition, complexes appear to be formed either during implantation or very rapidly during annealing for doses ? 3 × 10¹⁵ cm^?2. Data is presented which suggests that no inactive As complexes are formed in As implanted-annealed structures in which the maximum solubility of As⁺ ions is approached (3·8 × 10²⁰ atoms/cm³ at 1000°C, or a dose of 5–8 × 10¹⁵ cm^?2). This result pertains to the As dose used in this study. Since this result has not been observed in As-doped layers that were diffused from chemical sources, further work is needed in order to explain this anomaly.     

Impurity-induced disordering of AIGalnAs quantum wells by low temperature Zn diffusion

We investigated impurity-induced disordering (IID) in AIGalnAs multi-quantum wells (MQWs) on InP substrate by Zn diffusion under low temperature conditions. Blue-shift of band-gap energy of lattice-matched AIGalnAs MQW on InP strongly depended on the temperature of Zn diffusion. The lattice-matched MQW was not completely disordered below 500°C. On the other hand, photoluminescence spectra from compressively strained AIGalnAs MQW, after disordering was independent of the temperature of Zn diffusion. Considerable disordering was observed in the strained MQW, which was saturated even at the low temperature of 400°C. The measured hole concentration of the Zn diffused layer at 400°C was as low as 3 × l0¹⁸cm⁻³ The IID lasers were also fabricated and characterized. No significant increase in the optical loss due to the Zn diffusion was observed in these lasers. On leave from Toshiba Co., Japan.     

Ultralow‐Strain Zn‐Substituted Layered Oxide Cathode with Suppressed P2–O2 Transition for Stable Sodium Ion Storage

Layered transition metal oxides have drawn much attention as a promising candidate cathode material for sodium‐ion batteries. However, their performance degradation originating from strains and lattice phase transitions remains a critical challenge. Herein, a high‐concentration Zn‐substituted Na_xMnO₂ cathode with strongly suppressed P2–O2 transition is investigated, which exhibits a volume change as low as 1.0% in the charge/discharge process. Such ultralow strain characteristics ensure a stable host for sodium ion storage, which significantly improves the cycling stability and rate capability of the cathode material. Also, the strong coupling between the highly reversible capacity and the doping content of Zn in Na_xMnO₂ is investigated. It is suggested that a reversible anionic redox reaction can be effectively triggered by Zn ions and is also highly dependent on the Zn content. Such an ion doping strategy could shed light on the design and construction of stable and high‐capacity sodium ion host.     

Diffusion and solid solubility of Zn in GaP at 850°C

Zinc was diffused at 850°C from ternary sources containing 1–20 atom percent Zn and 0.5–1.0 atom percent P in Ga into n-type GaP grown by liquid phase epitaxy (LPE) and the liquid encapsulated Czochralski (LEC) process. Data on the surface concentration, and thereby the solid solubility of Zn as a function of the source composition, were obtained from⁶⁵Zn radiotracer analysis and electrical measurements. At 850°C these values range from 8×l0¹⁷ cm⁻³ for a 1 atom percent Zn to 5×10¹⁸ cm⁻³ for a 20 atom percent Zn concentration in the Ga/P/Zn ternary solution. These data are self-consistent, although they are somewhat lower than the previously reported values . Qualitatively, the results agree with recent thermodynamic calculations. The diffusion kinetics were found to be non-ideal as indicated by departures from a linear-square-root-of-time model and by reproducible changes in the junction depth following pre-diffusion heat treatments in different ambients.     

Comparison of Zn and Mg incorporation in MOVPE InP/GaInAsP laser structures

The objective of this work is to study the incorporation process of Zn in InP and related ternary and quaternary layers for long wavelength laser applications in comparison with the alternative acceptor Mg. In InP above a critical concentration of (1–2)×10¹⁸ cm^?3 a sudden onset of dopant diffusion during growth is observed for Zn and for Mg as well. This diffusion during growth can be markedly reduced by counter-doping with Si (Fermi level effect). Below the critical concentration Zn dopant profiles exhibit the same steep flanks as Mg dopant profiles suggesting the same low diffusion coefficients. However, Zn appears to be more suitable forp-type doping of InP, GaInAs and GaInAsP, because an accurate control of the dopant level in the epitaxial layers is easier to achieve with Zn than with Mg.     

A study of Zn diffusion in InP at low temperature

The diffusion of Zn in InP at low temperature is investigated. The experiment is accomplished in an evacuated and sealed quartz ampoule using Zn_eP₂ as the source of Zn. The electrical characteristics of the diffusion samples obtained by the isotemperature process and the two-temperature process have been compared. It is found that with the two-temperature process one can obtain a smooth, damageless and high-concentration surface layer. This process has been applied to fabricate InGaAsP/InP light emitting diodes, and the diodes obtained have an output power of ≥1mW with a series resistance of 2–5Ω. The behaviors of Zn diffusion in InP are discussed.