A review of the properties of hydrogen in crystalline semiconductors is presented. The equilibrium lattice positions of the various states of hydrogen are detailed, together with the reactions of atomic hydrogen with shallow and deep level impurities that passivate their electrical activity. Evidence for several charge states of mobile hydrogen provides a consistent picture for both the temperature dependence of its diffusivity and the chemical reactions with shallow level dopants. The electrical and optical characteristics of hydrogen-related defects in both elemental and compound semiconductors are discussed, along with the surface damage caused by hydrogen bombardment. The bonding configurations of hydrogen on semiconductor surfaces and the prevalence of its incorporation during many benign processing steps are reviewed. We conclude by identifying the most important areas for future effort.

Hydrogen in crystalline semiconductors

This paper presents a theoretical and experimental study of the recrystallization behavior of polycrystalline silicon films amorphized by self‐implantation. The crystallization behavior was found to be similar to the crystallization behavior of films deposited in the amorphous state, as reported in the literature; however, a transient time was observed, during which negligible crystallization occurs. The films were prepared by low‐pressure chemical vapor deposition onto thermally oxidized silicon wafers and amorphized by implantation of silicon ions. The transient time, nucleation rate, and characteristic crystallization time were determined from the crystalline fraction and density of grains in partially recrystallized samples for anneal temperatures from 580 to 640 °C. The growth velocity was calculated from the nucleation rate and crystallization time and is lower than values in the literature for films deposited in the amorphous state. The final grain size, as calculated from the crystallization param...

Recrystallization of amorphized polycrystalline silicon films on SiO2: Temperature dependence of the crystallization parameters

Thin layers of amorphous silicon (a‐Si) were produced by noble gas ion implantation of (100) substrates held at 77 K. Rutherford backscattering and channeling, and differential scanning calorimetry were used to measure the heat of crystallization, ΔHac, to be 11.9±0.7 kJ/mol, substantially less than the value predicted by scaling ΔHac of a‐Ge. The crystal growth velocity is found to have the form v=v0 exp(−2.24 eV/kT). We obtain a new estimate, 1420 K, for the melting temperature of a‐Si.

Heat of crystallization and melting point of amorphous silicon

The effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film is studied over the range 25–150 MHz. Deposition rates as high as 21 A/sec are obtained at ∼70 MHz, which is a factor of 5–8 larger than typical rates obtained for the conventional 13.56-MHz silane glow-discharge system. Only minor changes occur in the defect density (as measured by the photothermal deflection spectroscopy method), the optical bandgap, and the electrical conductivity over this frequency range. In a preliminaryinterpretation given here, the large variation of the deposition rate as a function of excitation frequency is explained in terms of changes in the electron energy distribution function.

Influence of plasma excitation frequency for a -Si:H thin film deposition

An insulated gate field effect transistor is constructed by first forming a non-single crystalline semiconductor layer or island on an insulating surface of a substrate. A gate insulating layer is then formed on the semiconductor layer. A gate electrode is formed on the gate insulating layer. An impurity is added to a portion of the semiconductor layer to form source and drain regions, and the semiconductor layer is irradiated with light through the gate insulating layer. In preferred embodiments, the substrate is maintained at a temperature less than 400° C. and the light have a wavelength of 250-600 nm.

Insulated gate field effect transistor and its manufacturing method

Amorphous silicon p‐i‐n diodes have been fabricated for the first time by chemical vapor deposition and post‐hydrogenation in a hydrogen plasma. By analyzing the current‐voltage characteristics we obtain current densities up to 50 A/cm2 and rectification ratios better than 107 for 3‐V applied bias. A characteristic reversible breakdown voltage is observed up to voltages of ∼20 V. These results are compared with those obtained on amorphous silicon p‐i‐n diodes prepared by glow discharge decomposition of SiH4.

High current post‐hydrogenated chemical vapor deposited amorphous silicon p‐i‐n diodes

Amorphous Si Schottky diodes are prepared by chemical vapor deposition and a post‐ hydrogenation treatment. Capacitance and photocurrent measurements on these diodes as a function of doping are discussed in terms of space‐charge characteristics and carrier collection mechanisms. For doped samples a full analysis of the C(ω) and C(V) dependences enables us to obtain the space‐charge width and the doping efficiency. A correlation between space‐charge width and collection length of photogenerated carriers is obtained in these samples. For undoped diodes the photocurrent versus wavelength dependences are used to analyze the collection efficiency. A power efficiency of 2.5% is obtained for a fully depleted cell without antireflection coating under AMl solar simulator conditions.

Post‐hydrogenated chemical vapor deposited amorphous silicon Schottky diodes

A nonlinear element consisting of two back‐to‐back platinum/a‐Si Schottky diodes made on amorphous silicon prepared by chemical vapor deposition of silane and post‐hydrogenation is described. Nonlinearity coefficients α of the I‐V characteristics (I=KVα) in the range 7–15 are obtained depending on doping and thickness of the active layer. The high multiplexing capacity (>1000 rows) at the television frame frequency is demonstrated, for the first time, by simulation on a single twisted‐nematic cell in series with the device.

New amorphous silicon nonlinear element for liquid crystal display addressing

We report a study of a‐Si:H films deposited in a hot‐wall glow‐discharge machine. Optical and transport properties were studied as a function of frequency (400 kHz and 13.56 MHz) and power of the radio frequency (rf), temperature and pressure during deposition, and they were found very similar to those of films deposited by other glow‐discharge techniques. Thin films (<1 μm) have a higher defect density than thicker films. The lowest defect density and disorder are achieved in the 200–250 °C temperature range. Pressure and rf frequency have no effect on defect density and disorder but control the position of the Fermi level. Reversible defect creation is induced by long and intense light irradiation but this induces no shift of the Fermi level.

A study of hydrogenated amorphous silicon deposited by hot‐wall glow discharge

Amorphous silicon TFTs have been realized using several plasma-CVD systems which differ in the conception of the reactor: hot or cold walls, and from the frequency used: 400 kHz and 13.56 MHz. Silicon nitride has been used as insulator. Inverted and direct staggered structures with different channel dimensions (0.5 ⩽ w/L ⩽ 20) are compared. High performance TFTs with mobility from 0.5 to 0.7 cm2v−1s−1 for inverted and from 0.1 to 0.4 cm2V−1s−1 for direct staggered TFTs have been optimized by a full study of the insulator semiconductor and source/drain contact properties.

J. Magariño

Papers

High current post‐hydrogenated chemical vapor deposited amorphous silicon p‐i‐n diodes

Post‐hydrogenated chemical vapor deposited amorphous silicon Schottky diodes

New amorphous silicon nonlinear element for liquid crystal display addressing

A study of hydrogenated amorphous silicon deposited by hot‐wall glow discharge

Dependence of a-Si:H TFTs Performances on Deposition and Process Parameters