Calorimetric study and thermodynamic description of Ga-Ge-Li liquid alloys

This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga_0.75Li_0.25)_1-xGe_x, (Ge_0.50Li_0.50)_1-xGa_x, (Ga_0.50Li_0.50)_1-xGe_x, (Ga_0.25Li_0.75)_1-xGe_x. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature.     

Advances in ion beam modification of semiconductors

This review provides an overview of the current status of ion-implantation research in silicon, germanium and the compound semiconductors SiC, GaN and ZnO. The discussion of silicon includes recent developments in metrology and device simulation, as well as a brief discussion of emerging applications in photovoltaics and quantum electronics. That of Ge includes a more detailed overview of doping, radiation damage and annealing processes due to the renewed research interest in this material. Finally, the discussion of compound semiconductors focuses on the newer wide bandgap materials where there are remaining implantation issues to be solved and potentially new implantation applications emerging.     

7815单液滴法萃取锗的动力学研究

在稀硫酸的锗盐中,使用7815萃取锗,对萃取动力学进行了研究。试验结果表明,初始锗的萃取速度受有机相和水相的接触面积、硫酸浓度和水相中锗浓度的影响,锗的萃取受扩散步骤控制。试验建立的萃取动力学方程是Jf=2.3×10-9[Ge]0.91[H+]0.32,相对标准误差为3.98%。     

High quality relaxed Ge layers grown directly on a Si(0 0 1) substrate

After a long period of developing integrated circuit technology through simple scaling of silicon devices, the semiconductor industry is now embracing technology boosters such as strain for higher mobility channel material. Germanium is the logical supplement to enhance existing technologies, as its material behaviour is very close to silicon, and to create new functional devices that cannot be fabricated from silicon alone (Hartmann et al. (2004) [1]). Germanium wafers are, however, both expensive and less durable than their silicon counterparts. Hence it is highly desirable to create a relaxed high quality Ge layer on a Si substrate, with the provision that this does not unduly compromise the planarity of the system. The two temperature method, proposed by Colace et al. (1997) [2], can give smooth (RMS surface roughness below 1 nm) and low threading dislocation density (TDD <10⁸ cm⁻²) Ge layers directly on a Si(0 0 1) wafer (Halbwax et al. (2005) [3]), but these are currently of the order of 1-2 μm thick (Hartmann et al. (2009) [4]).We present an in depth study of two temperature Ge layers, grown by reduced pressure chemical vapour deposition (RP-CVD), in an effort to reduce the thickness. We report the effect of changing the thickness, of both the low temperature (LT) and the high temperature (HT) layers, emphasising the variation of TDD, surface morphology and relaxation.Within this study, the LT Ge layer is deposited directly on a Si(0 0 1) substrate at a low temperature of 400 °C. This low temperature is known to generate monolayer islands (Park et al. (2006) [5]), but is sufficiently high to maintain crystallinity whilst keeping the epitaxial surface as smooth as possible by suppressing further island growth and proceeding in a Frank-van der Merwe growth mode. This LT growth also generates a vast number of dislocations, of the order of 10⁸-10⁹ cm⁻², that enable the next HT step to relax the maximum amount of strain possible. The effect of varying the HT layer thickness is studied by depositing on a LT layer of fixed thickness (100 nm) at a higher growth temperature of 670 °C. We find that the HT layer allows Ge-on-Ge adatom transport to minimise the surface energy and smooth the layer. The final step to the technique is annealing at a high temperature that allows the dislocations generated to glide, increasing the degree of relaxation, and annihilate. We find that annealing can reduce the TDD to the order of 10⁷ cm⁻², but at a cost of a significantly roughened surface.     

Bipolar switching characteristics of low-power Geo resistive memory

We reported an ultra low-power resistive random access memory (RRAM) combining a low-cost Ni electrode and covalent-bond GeO_x dielectric. This cost-effective Ni/GeO_x/TaN RRAM device has very small set power of 2 μW, ultra-low reset power of 130 pW, greater than 1 order of magnitude resistance window, and stable retention at 85 °C. The current flow at low-resistance state is governed by Poole-Frenkel conduction with electrons hopping via defect traps, which is quite different from the filament conduction in metal-oxide RRAM.     

InGaAs and Ge MOSFETs with high κ dielectrics

InGaAs and Ge MOSFETs with high κ’s are now the leading candidates for technology beyond the 15 nm node CMOS. The UHV-Al₂O₃/Ga₂O₃(Gd₂O₃) [GGO]/InGaAs has low electrical leakage current densities, C-V characteristics with low interfacial densities of states (D_it’s) and small frequency dispersion in both n- and p-MOSCAPs, thermal stability at temperatures higher than >850 °C, a CET of 2.1 nm (a CET of 0.6 nm in GGO), and a well tuning of threshold voltage V_th with metal work function. Device performances in drain currents of >1 mA/μm, transconductances of >710 μS/μm, and peak mobility of 1600 cm²/V s at 1 μm gate-length were demonstrated in the self-aligned, inversion-channel high In-content InGaAs n-MOSFETs using UHV-Al₂O₃/GGO gate dielectrics and ALD-Al₂O₃. Direct deposition of GGO on Ge without an interfacial passivation layer has given excellent electrical performances and thermodynamic stability. Self-aligned Ge p-MOSFETs have shown a high drain current of 800 μA/μm and peak transconductance of 420 μS/μm at 1 μm gate-length.     

Diffusion and doping issues in germanium

This paper gives a review on self- and dopant diffusion in germanium (Ge) under thermal equilibrium and irradiation conditions and specifies the underlying mechanisms of diffusion and the point defects involved. Diffusion in Ge under thermal equilibrium conditions is mainly controlled by vacancies. However, Ge interstitials mediate the diffusion under concurrent annealing and irradiation. This is verified by the diffusion behavior of self-atoms, boron, phosphorus and arsenic under proton irradiation. The diffusion under irradiation is explained with the property of the Ge surface that is proposed to be an insufficient sink for Ge interstitials. As a consequence, a supersaturation of self-interstitials is established during irradiation, whereas the vacancy concentration is kept at thermal equilibrium. This explains that under irradiation the diffusion of self- and dopant atoms via self-interstitials becomes visible that is otherwise negligible under conventional annealing conditions. Our findings demonstrate ways to switch between vacancy and self-interstitial mediated diffusion and shows new strategies in the diffusion doping of Ge for technological applications.     

Oxygen doped Ge crystals Czochralski-grown from the B2O3-fully-covered melt

Local vibrations of oxygen in Ge crystals grown from a melt fully covered by B₂O₃ were evaluated by Fourier-transform infrared spectroscopy. Ge single crystals containing oxygen were grown by the Czochralski method under various growth conditions. Oxygen concentrations in the crystals were determined to be in the range between 8.5 × 10¹⁵ and 5.5 × 10¹⁷ cm⁻³ from the infrared absorption at 855 cm⁻¹ originating in local vibration of Ge-O_i-Ge quasi-molecules. Absorption peaks relating to GeO_x, SiO_x and Si-O_i-Si were not detected in the as-grown crystals. The calibration coefficient for determining oxygen concentration in Ge crystals from the absorption peak intensity at 1264 cm⁻¹ was estimated to be 1.15 × 10¹⁹ cm⁻².     

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.     

Smooth, 3D Ge transistor channels by heteroepitaxial growth

Crystalline germanium (Ge) is a prime candidate as a material for high-performance transistors due to its higher electron and hole mobility with respect to those of silicon. In this study, we present a novel method of fabricating epitaxial Ge structures of high crystalline and morphological quality directly onto Si substrates, in which 3D Ge structures are grown by selective epitaxy then annealed in a hydrogen ambient at 850 °C. Under such annealing, the surface of the Ge structures deform by surface diffusion to form smooth, rounded shapes for which the surface energy is at a local minima. The apparent smoothness of the surface, along with the decreased defect density expected to exist in these heteroepitaxial Ge structures, suggest they are adequate for use as transistor channels.