The present paper reviews the results of experimental investigations of the photodoping of amorphous chalcogenides by metals, and in particular by silver. The kinetics of the photodissolution of the metal are described as also is the influence on the photodissolution rate of such factors as the wavelength and intensity of light, the composition and temperature of the semiconductor, and an external electric field. A separate section describes lateral diffusion. The properties of photodoped semiconductors (electrical, optical, photoelectric, etc.) are presented. The results in the literature are analysed, giving answers to such fundamental questions as the following. Where is the actinic light which is efficient for the photodissolution absorbed? Which is the diffusion-limiting step? What is the state of the diffusing species (neutral atoms or ions)? The dissolution of silver induced by electron or ion beams and the photodissolution of group II metals are mentioned. The experimental results are fol...

Photodoping of amorphous chalcogenides by metals

Methods of forming metal-doped chalcogenide layers and devices containing such doped chalcogenide layers include using a plasma to induce diffusion of metal into a chalcogenide layer concurrently with metal deposition. The plasma contains at least one noble gas of low atomic weight, such as neon or helium. The plasma has a sputter yield sufficient to sputter a metal target and a UV component of its emitted spectrum sufficient to induce diffusion of the sputtered metal into the chalcogenide layer. Using such methods, a conductive layer can be formed on the doped chalcogenide layer in situ. In integrated circuit devices, such as non-volatile chalcogenide memory devices, doping of the chalcogenide layer concurrently with metal deposition and formation of a conductive layer in situ with the doping of the chalcogenide layer reduces contamination concerns and physical damage resulting from moving the device substrate from tool to tool, thus facilitating improved device reliability.

Integrated circuit device and fabrication using metal-doped chalcogenide materials

The various photo-induced phenomena that occur in chalcogenide glasses are classified and described, with particular emphasis on the photo-dissolution effect. The detailed mechanisms responsible for many of these processes are still unknown, although in the case of photo-darkening in annealed a-As2S3 films, Raman experiments indicate that a light-induced change in the bond distribution from that for a chemically-ordered network towards one characteristic of a random network may be the principal cause. New results on the photo-dissolution of silver into As-S films are presented which indicate that the actinic radiation initiating the effect is absorbed in the photo-doped layer, close to the interface with the undoped region of the chalcogenide film. The basic mechanism responsible for the effect, however, is still not known.

Photo-induced structural and physico-chemical changes in amorphous chalcogenide semiconductors

A mechanism for the phenomenon of photodissolution of metals in amorphous chalcogenides is proposed which is based on the combined transport of ionic and electronic charge carriers during the photodissolution process. A parabolic law for the kinetics of this reaction is derived and the photoconductivity of the reaction product is the controlling factor for the rate. It is suggested that the site of the absorption of the actinic light is determined by the sign of the dominant electronic (photo) carriers in the reaction product.

A unified mechanism for metal photodissolution in amorphous chalcogenide materials

A model for the photodissolution of metals in amorphous chalcogenides is proposed, based on the simultaneous transport of metal ions and electronic charge carriers. A parabolic law for the kinetics of the process if derived; the photoconductivity of the reaction product is the controlling factor. It is suggested that the absorption site of the actinic light is determined by the sign of the dominant electronic (photo) carriers in the reaction product. The effect of pressure on the photodissolution rate can be readily understood within the framework of this model.

Photodissolution of metals in chalcogenide glasses : a unified mechanism

A new technique, measurement of the electrical resistance change of the Ag layer, is developed to study the kinetics of photodissolution of Ag in amorphous As2S3. It is shown that the photodissolution rate is proportional to the light intensity absorbed in the As2S3 at the As2S3Ag interface, but photoelectrons ejected from the Ag into the As2S3 also contribute. The process is shown to be two-stage. Firstly a critical “radiation damage” dose must be accumulated in the As2S3. Secondly, the Ag atom is photon-assisted across the As2S3Ag interface activation barrier.

D. Goldschmidt

Papers

The kinetics of photodissolution of Ag in amorphous As2S3 films