Simulation of low-temperature arsenic diffusion from a heavily doped silicon layer

Low-temperature (500–800°C) diffusion of As from a heavily doped Si layer was simulated on the basis of a dual pair mechanism. The anomalously high diffusion rate is attributed to excess self-interstitials accumulated in the layer during the preceding high-temperature diffusion stage. The shift of the concentration profile in the region of intermediate values of concentrations is caused by the presence of a maximum in the concentration dependence of the diffusivity. This shift is attributed to the considerable role that negatively charged self-interstitials play in the arsenic diffusion process (f _I ^? ≈0.4).     

Minority carrier diffusion length in liquid epitaxial GaP

Using a Schottky diode photocurrent technique, investigations have been made of the room temperature value of minority carrier diffusion length in liquid epitaxial GaP grown on both (111) and (100) oriented pulled GaP substrates. Results are presented for undoped layers and layers doped separately with S, S and N, Te, Zn, and Zn and O, to cover a range of impurity concentration in the GaP. The measured values of minority carrier diffusion length are found to depend on the concentration of the dominant impurity and, for the undoped and Zn doped layers, also on the growth orientation of the substrate. From the dependence of the minority carrier diffusion length on majority carrier concentration we infer the dominant room temperature recombination process in the layers. In our undoped layers this process is believed to correspond to recombination via residual Si substituted on P sites. In Te, S, Zn, and Zn, O doped layers the dominant recombination mechanism can be attributed to a non-radiative band-band Auger process, although in the case of the Zn, O doped layers a competing recombination process is observed which is believed to correspond to recombination via centres formed by unpaired O and Zn defects. The lifetime for this competing process is predicted to be sensitive to annealing.     

InP/InGaAs double-heterojunction bipolar transistors grown on (100)Si by metalorganic chemical vapor deposition

The authors report the successful fabrication of InP/InGaAs double-heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates. The Si substrates used were p-type (boron doped) FZ grown wafers with a resistivity of 5000 Ω×cm, oriented 2° off the (100) plane toward the [110] direction. Epitaxial layers for DHBTs were grown on the Si substrate with a thin GaAs buffer layer. A two-step growth process was applied for the InP layers on GaAs-on-Si wafers. The transistors exhibit high current gains over 200, which is comparable to those in transistors grown on InP substrates. The dislocations are found to increase the recombination current very little in the neutral base region, but increase in generation-recombination current at the emitter-base interface     

A two-dimensional model for the excess interstitial distribution in silicon during thermal oxidation

A steady-state solution for the partial differential equation governing the two-dimensional distribution of the excess interstitials during thermal oxidation of silicon was obtained using a finite difference method. It is assumed that the excess interstitials at the unoxidizing Si-SiO2interface are annihilated at a rate proportional to the excess interstitial concentration at the interface and the surface recombination velocity of the excess interstitials. Lin et al.'s experimental observation that the lateral diffusion length of the excess interstitials under the unoxidizing Si-SiO2interface is much shorter than the vertical diffusion length in the bulk can be explained by this interface annihilation model. Surface recombination velocity divided by the bulk diffusivity of self-interstitials in silicon at the Si-SiO2interface is found to be about 0.4-1.0/µm within the oxidation temperature range between 900° and 1100°C.     

The influence of sinks of intrinsic point defects on phosphorus diffusion in Si

The influence of sinks associated with structural defects is analyzed qualitatively based on the model of P diffusion in Si by the dual pair mechanism. It is demonstrated that the allowance made for sinks of self-interstitials leads to the retardation of the enhanced P diffusion for the low-content region in the tail of the concentration profile. The influence of sinks is most pronounced if the position of their peak concentration is in the region of the peak of generation of self-interstitials inside the diffusion layer. From a comparison of the result of calculations with the experimental data, the parameters of the capture of self-interstitials by structural defects, which are introduced by the P diffusion and implantation of electrically inactive Ge and N impurities, are determined.     

Efficient silicon heterojunction solar cells based on p‐ and n‐type substrates processed at temperatures < 220°C

We present the optimization and characterization of heterojunction solar cells consisting of an amorphous silicon emitter, a single crystalline absorber and an amorphous silicon rear side which causes the formation of a back surface field (a‐Si:H/c‐Si/a‐Si:H). The solar cells were processed at temperatures <220°C. An optimum of the gas phase doping concentration of the a‐Si:H layers was found. For high gas phase doping concentrations, recombination via defects located at or nearby the interface leads to a decrease in solar cell efficiency. We achieved efficiencies >17% on p‐type c‐Si absorbers and >17·5% on n‐type absorbers. In contrast to the approach of Sanyo, no additional intrinsic a‐Si:H layers between the substrate and the doped a‐Si:H layers were inserted. Copyright © 2006 John Wiley & Sons, Ltd.     

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.     

SiO_x、Si/Si_(1-x)Ge_x的横向磁阻和迁移率的无接触测量

用分子束外延技术在ｐ型Ｓｉ衬底上生长成了Ｓｉ／Ｓｉ１－ｘＧｅｘ应变层超晶格和掺铒（Ｅｒ）ＳｉＯｘ外延层，用无接触法测量了它们的横向磁阻，并且用拟合方法由横向磁阻计算了它们的迁移率。     

Experimental and simulated analysis of front versus all‐back‐contact silicon heterojunction solar cells: effect of interface and doped a‐Si:H layer defects

Front silicon heterojunction and interdigitated all‐back‐contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high efficiency and low cost because of their good surface passivation, heterojunction contacts, and low temperature fabrication processes. The performance of both heterojunction device structures depends on the interface between the crystalline silicon (c‐Si) and intrinsic amorphous silicon [(i)a‐Si:H] layer, and the defects in doped a‐Si:H emitter or base contact layers. In this paper, effective minority carrier lifetimes of c‐Si using symmetric passivation structures were measured and analyzed using an extended Shockley–Read–Hall formalism to determine the input interface parameters needed for a successful 2D simulation of fabricated baseline solar cells. Subsequently, the performance of front silicon heterojunction and IBC‐SHJ devices was simulated to determine the influence of defects at the (i)a‐Si:H/c‐Si interface and in the doped a‐Si:H layers. For the baseline device parameters, the difference between the two device configurations is caused by the emitter/base contact gap recombination and the back surface geometry of IBC‐SHJ solar cell. This work provides a guide to the optimization of both types of SHJ device performance, predicting an IBC‐SHJ solar cell efficiency of 25% for realistic material parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Decrease in the binding energy of donors in heavily doped GaN:Si layers

The properties of Si-doped GaN layers grown by molecular-beam epitaxy from ammonia are studied by photoluminescence spectroscopy. It is shown that the low-temperature photoluminescence is due to the recombination of excitons bound to donors at Si-atom concentrations below 10¹⁹ cm^?3. At a Si-atom concentration of 1.6 × 10¹⁹ cm^?3, the band of free excitons is dominant in the photoluminescence spectrum; in more heavily doped layers, the interband recombination band is dominant. A reduction in the binding energy of exciton-donor complexes with increasing doping level is observed. With the use of Haynes rule, whereby the binding energy of the complex in GaN is 0.2 of the donor ionization energy E _D , it is shown that E _D decreases with increasing Si concentration. This effect is described by the dependence {ie1134-1}, where E _D ^otp is the ionization energy of an individual Si atom in GaN. The coefficient that describes a decrease in the depth of the impurity-band edge with increasing Si concentration is found to be α = 8.4 × 10^?6 meV cm^?1.     

A model of high-and low-temperature phosphorus diffusion in silicon by a dual pair mechanism

A model of phosphorus diffusion in silicon was developed on the basis of a dual pair mechanism; according to this model, the contribution of the impurity-vacancy (PV) and impurity-self-interstitial (PI) pairs to diffusion is accounted for directly in terms of the phosphorus diffusion coefficient. A violation of thermodynamic equilibrium in relation to native point defects occurs as a result of diffusion of the PI neutral pairs. At the high-temperature diffusion stage, the phosphorus diffusion is described by a single diffusion equation with the diffusion coefficient dependent on both the local and surface phosphorus concentrations; whereas at the next (occurring at lower temperatures) stage, the phosphorus diffusion is described by two diffusion equations for the total concentrations of the components containing phosphorus and self-interstitials. An anomalously high rate of the low-temperature diffusion is ensured by excess self-interstitials accumulated in the doped layer during the preceding high-temperature diffusion. The model makes it possible to quantitatively account for the special features of the phosphorus diffusion in a wide range of the surface concentrations at both the high (900–1100°C) and lower (500–700°C) temperatures.     

Measurement of surface recombination velocity and bulk lifetime in Si wafers by the kinetics of excess thermal emission

A contactless nondestructive technique for measuring recombination parameters (surface recombination velocity and bulk and effective lifetime of free carriers) in Si wafers is proposed. The technique is based on the analysis of the relaxation kinetics of excess thermal emission of a wafer beyond the Si intrinsic absorption edge (λ > 3 μm) after excitation by a short laser pulse with a photon energy higher than the Si band gap. Experimental results for wafers 300 μm and 2 mm thick, excited by laser radiation with wavelengths of 0.96 and 1.06 μm at above-room temperatures are presented. The surface and bulk components of the effective lifetime are separated by extrapolating the final portion of the kinetics of excess thermal emission relaxation to the intersection with the y coordinate axis.     

Influence of surface recombination on the burn-in effect inmicrowave GaInP/GaAs HBT's

In this paper, we report on the early increase of the dc current gain (burn-in effect) due to the electrical stress of carbon doped GaInP/GaAs heterojunction bipolar transistors (HBTs). Devices featuring different passivation layers, base doping, and emitter widths were investigated. The obtained data demonstrate that the burn-in effect is due to a reduction of the surface recombination located at the extrinsic base surface, around the emitter perimeter. It is concluded that the recombination centers are related to defects at the passivation/semiconductor interface and that, during the stress, they are passivated by hydrogen atoms released from C-H complexes     

Effect of oxygen injection during vpe growth of GaAs Films

The effect of oxygen injection during VPE growth of silicon doped and unintentionally doped GaAs has been investigated for the Ga-AsCl₃-H₂ process. Depending on the oxygen concentration a reduction in the carrier concentration of up to four orders of magnitude is found for the case of Si doping. Without purposely adding Si, oxygen injection yields high resistivity layers. Hall mobility data suggest that the simultaneous injection of both silicon and oxygen is also responsible for the introduction of a deep center which is probably associated with a Si-0 complex. We compared our results on carrier concentration with values calculated from a thermody-namic model in which both the injected SiH₄ and oxygen are taken into account. The computed behavior shows the same trend as our experimental data. This finding also provides further support for the validity of the silicon contamination model as an explanation of the background doping of VPE GaAs.     

High mobility GaAs-AlxGa1?xAs single period modulation-doped heterojunctions

Single period modulation-doped structures composed of an AlxGa1?xAs layer, part of which is doped with Si, on top of an undoped GaAs layer have been grown by molecular beam epitaxy. The films were characterised using Hall effect measurements carried out at temperatures between 10 and 300 K. With 50?75 ? thick undoped (Al, Ga)As layers near the interface, mobilities in excess of 115000 cm2/Vs at 10 K and 7450 cm2/Vs at 300 K have been achieved for an average doping concentration of ?5×1016 cm?3. These are some of the highest mobilities as yet obtained from modulation-doped structures, and represent an increase in mobility over equivalently doped GaAs by about a factor of 20 at 10 K and by a factor of 2 at 300 K.     

Die rekombination in thyristoren und gleichrichtern aus silizium: Ihr einfluss auf die durchlasskennlinie und das freiwerdezeitverhalten

The influence of the recombination properties of the different silicon layers in power rectifiers and thyristors on the forward characteristic and the dynamic behaviour is discussed quantitatively, taking into account Auger-recombination. This leads to more exact dimensioning guidelines for the development of technical devices. Measurement methods that permit an independent determination of the recombination properties of the individual silicon layers are discussed and measurement results are given. For the recombination parameters h of the highly doped boundary regions we obtained values between 1 · 10^?14 and 6 · 10^?14 cm⁴ sec^?1 fairly uniformly, independent of the method of preparation (alloyed or diffused). This is in accord with h-values that were found with differently prepared emitters of transistors for communication purposes. The possibilities to improve the specification combination of power devices that could be expected as a result of a reduction of these recombination parameters h are quantitatively discussed.     

Measurement of recombination lifetime profiles in epilayers using a conductivity modulation technique

A new experimental techique is described to accurately measure the recombination lifetime profile in lightly doped epitaxial layers of thickness less than the minority-carrier diffusion length. This technique requires the use of a particular "test" structure composed of a lateral p⁺-n-n⁺diode on the surface of the epilayer and a control electrode on the substrate layer. Using a conductivity modulation technique, the proposed measurement method is independent of recombination effects in the highly doped regions needed for every test structure. Moreover, the evaluation of lifetime profiles along the epilayer is made possible by varying the width of the conductivity modulated region through the control electrode bias. The measurement theory is developed for the high-injection regime, usually applicable to the lightly doped layers of bipolar power devices.     

N-type doping of 4H-SiC with phosphorus Co-implanted with C or Si

Phosphorus has been shown to be a much better dopant than nitrogen in 4H−SiC for heavily doped n-type implantation. In this paper, the effect of co-implantation of phosphorus with carbon or silicon is studied. The implanted layers are characterized by an analytical technique (secondary ion mass spectrometry). Electrical measurements include sheet resistance and Hall measurements as well as forward and reverse I–V characterization of the resulting n+/p rectifiers. The effect of co-implantation of P/C and P/Si on the electrical activation of phosphorus has been monitored. After 1700°C anneal, respective sheet resistance values of 111 and 132 ohm/square were measured. Forward characteristics of these diodes are observed to obey a generalized Sah-Noyce-Shockley multiple level recombination model with four shallow levels and one deep level.     

Influence of dislocations on the DC characteristics of AlGaAs/GaAsheterojunction bipolar transistors

The influence of dislocations on the minority electron lifetime in p-type GaAs layers and on AlGaAs/GaAs HBTs has been investigated. The minority electron lifetime in 1×10¹⁹/cm³ doped p-GaAs decreases significantly when the dislocation density is greater than 10⁷/cm². This result agrees well with analysis of carrier transport in highly dislocated material. Current gain reduction in HBTs with high dislocation density is found to be due to two effects: reduction of the electron lifetime in the base layer and an increase of the recombination current in the emitter-base junction depletion region. These two effects are comparable in reducing the current gain     

Influence of the Growth Conditions and Doping Level on the Luminescence Kinetics of Ge:Sb Layers Grown on Silicon

Semiconductors - The emission properties of Ge layers grown on Si(001) substrates and doped with Sb to different levels are studied by means of steady-state and time-resolved photoluminescence...