Thermal degradation of compound single crystal substrates (e.g., InP) containing a relatively volatile element (e.g., P) prior to LPE growth has been virtually eliminated by an improved protection technique. A partial pressure of the volatile element is provided by a solution (e.g., Sn-In-P) localized inside a chamber which is external to the LPE boat and which surrounds substrate prior to growth, thereby preventing thermal damage to the substrate surface. Applicability of the technique to other epitaxial growth processes (e.g., VPE and MBE) is also discussed.
A process for producing a semi-insulating InP single crystal and a semi-insulating InP single crystal are disclosed. The process comprises: a first step heat-treatment for heating an undoped InP single crystal having a concentration of a residual impurity of 0.05 ppmw or less containing at least one of Fe, Co and Cr, at a temperature of not less than 930.degree. C. and less than 1000.degree. C. in an atmosphere of phosphorous vapor pressure in the ampoule which is not less than a dissociation pressure of InP in equilibrium at the temperature and which is not more than 15 atm; and a second step heat-treatment for thereafter heating the InP single crystal at a temperature of not less than 662.degree. C. and less than 900.degree. C. in an atmosphere of phosphorous vapor pressure in the ampoule which is not less than 5 atm nor more than 50 atm. The semi-insulating InP single crystal substrate has a uniformity of mobility not more than 10% on the surface of the substrate.
An interrupted liquid phase epitaxy process for producing distributed feedback laser wafers involves epitaxial growth at a first temperature range followed by epitaxial growth at a second higher temperature range. A prior art liquid phase epitaxy process involves a low temperature soak at a temperature of approximately 615 degrees Centrigrade followed by ramped cooling and epitaxial growth of a guiding layer, active layer and confining layer at a temperature of approximately 595 degrees Centigrade. The interrupted liquid phase epitaxy process involves epitaxial growth of a guiding layer in a manner similar to the prior art process, but growth of the guiding layer is followed by a high temperature soak at a temperature of approximately 645 degrees Centrigrade. Ramped cooling follows, with epitaxial growth of the active layer and confining layer taking place at a temperature of approximately 628 degrees Centigrade. Epitaxial growth at the higher temperature reduces difficulties with spinodal decomposition and allows improved control over the amount of phosphorus used in the process.
A method of supplying scents to a room of a motor-car. In this method, a scent holder is provided within the room of the motor vehicle, the scent holder containing scents bearing materials for emitting different scents useful for a driver of the motor vehicle. Reference data for respective driving conditions of the motor vehicle are stored, the reference data indicating need for supply of respective scents. After storing the reference data, a driving condition of the motor vehicle is detected for producing an electric drive signal representing the driving condition. The drive signal thus produced is compared with a corresponding reference datum for determining whether or not the detected driving condition requires one of the scents contained in the scent holder. When the detected driving condition requires the one scent, one scent bearing material containing the one scent is selected. Then, the one scent from the one scent bearing material is supplied to the room of the motor vehicle.
