Diffusion and activation of phosphorus in germanium

In this work we investigate the diffusion and the activation behavior of implanted phosphorus in Ge. We used both conventional thermal processing as well as laser annealing by pulsed ns Nd–YAG laser. Chemical profiles were obtained by secondary-ion-mass spectrometry (SIMS) and sheet resistance was estimated by Van der Pauw method. These measurements demonstrated a box-shaped dopant profile for both conventional and laser annealed samples which are in agreement with other research reports indicating enhanced dopant diffusivity. From these experiments and critical comparison with other studies we conclude about the value of the intrinsic diffusion coefficient and we discuss the validity of the doubly charged vacancy model in simulating our experiments. To more accurately account for these parameters we have also implemented a pileup and a segregation model to simulate the dopant loss due to outdiffusion of phosphorus during the annealing process. In order to understand the influence of defects on transient dopant diffusion as well as on outdiffusion we have also annealed P implanted Ge prior to conventional annealing with laser above melting threshold to eliminate ion implantation defects as these are monitored by transmission electron microscopy.     

Simultaneous diffusion of Si and Ge in isotopically controlled heterostructures

Experiments on the diffusion of Si and Ge in Si_1-xGe_x-isotope heterostructures with Ge contents x=0, 0.05, and 0.25 were performed at temperatures between 870 and . The concentration profiles of the stable Si- and Ge-isotopes were recorded by means of time-of-flight secondary ion mass spectrometry. For all compositions, an Arrhenius type temperature dependence of diffusion was observed. The activation enthalpy of Si diffusion in SiGe equals the activation enthalpy of Ge diffusion and the pre-exponential factors agree within experimental accuracy. However, the absolute values of the Si and Ge diffusion coefficients indicate a clear trend. In elemental Si the diffusion coefficients of Si and Ge agree, but the difference between the diffusion coefficients of Ge and Si in Si_1-xGe_x increases with x. This indicates that with increasing Ge content the diffusional jumps of Ge atoms become more successful compared to that of Si. This trend is explained with an increasing contribution of vacancies to self-diffusion in Si_1-xGe_x with an increase of the Ge content x.     

Ab-initio simulation of self-interstitial in germanium

Density functional theory (DFT) with local density approximation including on-site Coulomb interaction (LDA+U) has been used to calculate the formation energy of the neutral and charged self-interstitial in germanium as a function of the Fermi level. The calculations suggest that the self-interstitial in germanium can exist in four different charge states: 1–, and 0 for the 1 1 0 split interstitial, 0, 1+, and 2+ for the tetrahedral position. The 1 1 0 split interstitial acts as an acceptor, while the tetrahedral self-interstitial acts as a double donor. Allowing structural changes of the self-interstitial with the charge state, the existence of a “two-state defect” in low-temperature irradiated p-type Ge can be explained.     

Connecting bulk properties of germanium with the behavior of self- and dopant diffusion

The understanding of self- and dopant diffusion properties over a range of temperatures and pressures can be technologically important for the formation of defined and efficient nanoelectronic devices. Phosporous, Arsenic and antimony are n-type dopants that can be considered for n-channel germanium metal oxide semiconductor field effect transistors. Using recent experimental data we show that elastic and expansivity data can reproduce the self-diffusion and n-type dopant diffusion coefficient of germanium in the temperature range 702–1177 K. This is achieved in the framework of the cBΩ model, which assumes that the defect Gibbs energy is proportinal to the isothermal bulk modulus and the mean volume per atom.     

Complexes of self-interstitials with oxygen atoms in germanium

Interactions of germanium self-interstitials with interstitial oxygen atoms in Ge crystals have been studied by combining experimental and theoretical methods. Self-interstitials were created in oxygen-rich Ge crystals by irradiation with MeV electrons at 80 K, and I–O-related complexes were studied by means of infrared absorption spectroscopy, while the density functional theory was used to model structures, local vibrational modes and electronic properties of IO and I₂O centers. It is argued that two absorption lines at 674 and 602 cm⁻¹, which develop upon annealing of irradiated Ge:O crystals in the temperature range 180–220 K, are related to IO complexes, while another set of bands at 713 and 803 cm⁻¹ is related to I₂O. Those assignments are supported by the comparison with the calculated local vibrational modes of the defects.     

Formation of Nickel Oxide Nanotubes with Uniform Wall Thickness by Low‐Temperature Thermal Oxidation Through Understanding the Limiting Effect of Vacancy Diffusion and the Kirkendall Phenomenon

In this work, the step‐wise oxidation mechanism of nickel (Ni) nanowires is elucidated. Rapid vacancy diffusion plays a significant role at low temperatures in forming heterostructures of nickel oxide (NiO) nanotubes with Ni nanowires. Subsequent investigations of Ni nanowire oxidation at higher temperatures and faster temperature ramp rates show that it is difficult to bypass this rapid vacancy diffusion stage, which affects the formation of the final structure. Therefore, it is unlikely to form solid NiO nanowires or NiO nanotubes with uniform wall thickness through the conventional annealing/oxidation process of Ni nanowires. Instead, a step‐wise oxidation process by combining low temperature oxidation with a chemical etching step is utilized to produce for the first time NiO nanotubes with uniform wall thickness from Ni nanowires.     

Carrier effective mobilities in germanium MOSFET inversion layer investigated by Monte Carlo simulation

This paper presents the Monte Carlo studies of inversion mobility in Ge MOSFETs covering a wide range of bulk-impurity concentrations (10¹⁴ cm⁻³–10¹⁷ cm⁻³), and substrate bias (0–10 V). Carrier mobilities in Ge MOSFETs have obviously increased compared with those in Si MOSFETs. At low effective field, both electron and hole mobilities have increased over 100%; while at high effective field the increase is reduced due to the effect of surface roughness. Similar to Si MOSFETs, the carrier effective mobilities in Ge MOSFETs also have a universal behavior. The universality of both electron and hole mobilities holds up to a bulk-impurity concentration of 10¹⁷ cm⁻³. On substrates with higher bulk-impurity concentrations, the carrier effective mobilities significantly deviate from the universal curves under low effective field because of Coulomb scattering by the bulk impurity.     

Electrical passivation by hydrogen plasma treatment of transition metal impurities in germanium

Transition metal impurities in germanium introduce deep levels in the band gap, which may influence the lifetime of carriers and leakage currents of devices. In this work it is shown that Ti, Cr and Fe centres in germanium can be passivated using plasma hydrogenation. The metals have been implanted at 90 keV in n- and p-type wafers and in-diffused during a 5 min thermal anneal at 500 °C. Samples have been hydrogenated using a DC plasma for 4 h at 200 °C and Schottky diodes were made for measurement using DLTS. It is found that the levels of metal impurities are passivated by hydrogenation. Characteristic hole and electron traps are assigned to the irradiation damage induced by the direct plasma exposure. Metal-specific levels are tentatively assigned to transition metal–hydrogen-related centres. Two hole traps at 0.05 and 0.10 eV above the valence band are only present in the Cr-doped samples and are tentatively assigned to chromium–hydrogen complexes. A comparison is made with copper–hydrogen in germanium.     

Doping of semiconductors by molecular monolayers: monolayer formation,dopant diffusion and applications

The continuous miniaturization in the semiconductor industry brings electronic devices with higher performance at lower cost. The doping of semiconductor materials plays a crucial role in tuning the electrical properties of the materials. Ion implantation is currently widely used. Yet, this technique faces challenges meeting the requirements for smaller devices. Monolayer doping (MLD) has been proposed as one of the alternative techniques for doping semiconductors. It utilizes dopant-containing organic molecules and grafts them onto semiconductor surfaces. The dopant atoms are subsequently driven into the substrate by high temperature annealing. MLD has shown the capability for ultra-shallow doping and the doping of 3-D structures without causing crystal damage. These features make this technique a promising candidate to dope future electronic devices. In this review the processes for monolayer formation and dopant incorporation by annealing will be discussed, as well as the applications of MLD in device fabrication.     

Density-functional theory study of Au, Ag and Cu defects in germanium

Gold, silver and copper defects in germanium are modeled using density functional theory. The structures and electrical properties of the substitutional metals are calculated in excellent agreement with experiment. Interstitial Au, Ag and Cu are found to be shallow donors, in disagreement with a previous assignment of Cu_i to a hole trap in the lower half of the gap. Substitutional–interstitial metal (M_i–M_s) pairs and metal–vacancy pairs (M_s–V) are also investigated.     

应用于扩散工艺中的闭管扩散技术

介绍了一种用于晶体硅太阳能电池p-n结制造的闭管扩散技术,它主要是针对目前使用的开管扩散技术的不足而提出的,实践证明,该技术不仅扩散均匀性优,而且节源、节能、环保,同时它还可以运用于其它半导体材料的扩散掺杂工艺。     

Ab initio investigation of phosphorus and boron diffusion in germanium

P and B diffusion has been modeled in Ge using ab initio methods along with the formation energies and electrical levels of various P_xV_y defects expected to be important in the deactivation of P in heavily n-doped Ge. The calculated activation barrier for B diffusion is found to be substantially lower than the measured barrier. However, the exceptionally large pre-exponential factor in the measured diffusivity points to a Meyer–Neldel rule operating and accounting for the discrepancy. The magnitude of the theoretical diffusivity is about a factor 10 lower than observed. For P diffusion, the experimental and theoretical results are in much closer agreement. The formation energy calculations show that all P_xV_y clusters are stable with respect to their component defects, and all but P₄V are predicted to introduce acceptor levels into the band gap. A simple analysis of possible formation mechanisms and Coulombic contributions suggests that as in Si, P₃V is the most important compensating center in heavily n-doped Ge.     

Shallow boron implantations in Ge and the role of the pre-amorphization depth

The impact of the Ge pre-amorphization conditions on shallow B profiles, resulting from a 1 keV implantation in n-type Ge and a 500 °C 1 min rapid thermal anneal, is investigated. In general, an increase of the sheet resistance with lower Ge energy is observed. There is some evidence for tail diffusion, enhancing slightly the junction depth and reducing its steepness. This could point to end-of-range-mediated transient-enhanced diffusion (TED) of B in Ge. It is clear that for this to happen, a pre-amorphization is required which contains completely the B profile.     

High performance n/p and p/n germanium diodes at low-temperature activation annealing

In this work we demonstrate the fabrication and characterization of high performance junction diodes using annealing temperatures within the temperature range of 300-350 °C. The low temperature dopant activation was assisted by a 50 nm platinum layer which transforms into platinum germanide during annealing. The fabricated diodes exhibited high forward currents, in excess of 400 A/cm² at ∼|0.7| V for both p⁺/n and n⁺/p diodes, with forward to reverse ratio I_F/I_R greater than 10⁴. Best results for the n⁺/p junctions were obtained at the lower annealing temperature of 300 °C. These characteristics compare favorably with the results of either conventional or with Ni or Co assisted dopant activation annealing. The low-temperature annealing in combination with the high forward currents at low bias makes this method suitable for high performance/low operating power applications, utilizing thus high mobility germanium substrates.     

射频功率和衬底温度对碳化锗膜中sp3杂化碳原子的影响

利用磁控溅射方法以CH4和Ar的混合放电气体溅射单晶Ge靶制备碳化锗(Ge1-xCx)薄膜,通过XPS、Raman和Nanoindentation等表征手段系统地研究了射频功率和衬底温度对所获薄膜成分、键合结构及力学性质的影响。研究发现:射频功率和衬底温度的增加均能提高膜中的Ge含量,这分别归因于Ge溅射产额的增加以及含碳基团在衬底上脱附作用的增强。Ge含量的增加促进了sp2C-C键转变为sp3Ge-C键,进而显著提高了膜中sp3杂化碳原子的相对含量并改善了Ge1-xCx薄膜的硬度。这些结果表明:提高射频功率和衬底温度是制备富含sp3C的硬质碳化锗薄膜的有效途径。     

铜蒸气激光器扩散系数的研究

推导了铜蒸气激光器带电粒子的双极扩散系数。结合铜蒸气激光器动力学模型对铜蒸气激光器动力学过程中的铜亚稳态粒子热扩散去激发及带电粒子双极扩散进行了分析。定量地给出了粒子热扩散项对铜亚稳态粒子密度及电子的双极扩散对电子密度的影响。     

Diffusion of phosphorus in CdTe

The diffusion of phosphorus in CdTe was measured as a function of anneal time and temperature in the temperature range 600–900°C. The diffusion anneals were carried out in evacuated silica capsules mainly with traces of radioactive phosphorus in the capsule along with sufficient cadmium metal to maintain a saturated vapor pressure over the CdTe slice throughout each anneal. The concentration profiles were measured using a radiotracer sectioning technique. Diffusion anneals were carried out also using other conditions, including some with excess tellurium in the capsule in place of the cadmium. The diffusion profiles were single component. The standard erfc function gave satisfactory fits to the profiles which were Fickian in nature except for short anneal times at intermediate temperatures. When the diffusivity was plotted on an Arrhenius graph, a straight line was obtained giving an activation energy of 2.0 eV. The surface concentration at each temperature was independent of time and varied in value between 1.5×10¹⁶ cm⁻³ at 600°C to 1×10¹⁸ cm⁻³ at 900°C. When the results were plotted on an Arrhenius graph, the results gave a straight line with an activation energy of 1.3 eV.     

Understanding the effect of triplet sensitizers in organic photovoltaic devices

The effect of PtOEP as a dopant on the performance of MEH-PPV/C₆₀ photovoltaic devices was studied. Bilayer heterojunction devices with various compositions and layer structures were used to determine the possible pathways by which the photogeneration efficiency is enhanced. A key finding is that photocurrent generation enhancement always occurs in the MEH-PPV absorption region, regardless of the PtOEP dopant concentration or the MEH-PPV layer thickness. This result suggests that the presence of PtOEP in the donor MEH-PPV layer is primarily responsible for increasing the triplet exciton diffusion length of MEH-PPV by acting as a triplet sensitizer, rather than as an additional absorber for direct photogeneration. Values obtained from simulation show that the enhancement of exciton diffusion length of MEH-PPV can be more than a factor of 2 with optimal PtOEP concentrations. Further support for the role of PtOEP as a triplet sensitizer in MEH-PPV was obtained in experiments incorporating a blocking layer between MEH-PPV and C₆₀, whereby the various exciton transfer processes can be differentiated.     

新颖的功率半导体器件RSD及其应用

反向开通可控硅二极管是一种近年来发展起来的新型半导体功率开关器件,具有很强的导流能力。在大功率固态化电源应用中,具有很大的优势。本文分析了这种器件的构造及工作机理,并说明其应用。