Abstract: A Light-emitting diode having improved moisture resistance characteristics comprises a p-type gallium arsenide substrate and four epitaxial layers of Al.sub.x Ga.sub.1-x As (22, 23, 24 and 25). These epitaxial layers comprises an intervening layer (22) of p-type Al.sub.x1 Ga.sub.1-x1 As, a cladding layer (23) of p-type Al.sub.x2 Ga.sub.1-x2 As, an active layer (24) of Al.sub.x3 Ga.sub.1-x3 As, and a window layer (25) of Al.sub.x4 Ga.sub.1-x4 As so as to form a double-hetero structure, where x1, x2, x3 and x4 represent mixed crystal ratios of aluminum to arsenic of the layers, respectively, and meet the condition that:x2.gtoreq.x4>x1.gtoreq.x3 (0.ltoreq.x1, x2, x3, x4.ltoreq.1).

Abstract: A light-emitting diode having improved moisture resistance characteristics comprises a p-type gallium arsenide substrate and four epitaxial layers of Al.sub.x Ga.sub.1-x As (22, 23, 24 and 25). These epitaxial layers comprises an intervening layer (22) of p-type Al.sub.x Ga.sub.1-x As, a cladding layer (23) of p-type Al.sub.x2 Ga.sub.1-x2 As, an active layer (24) of Al.sub.x3 Ga.sub.1-x3 As, and a window layer (25) of Al.sub.x4 Ga.sub.1-x4 As so as to form a double-hetero structure, where x1, x2, x3 and x4 represent mixed crystal ratios of aluminum to arsenic of the layers, respectively, and meet the condition that:x2.gtoreq.x4>x1.gtoreq.x3 (0.ltoreq.x1, x2, x3, x4.ltoreq.1).

Abstract: This invention relates to a hardening material for medical and dental use which is composed of a powder of calcium phosphate and a hardening liquid.A subject of the present invention is to provide a hardening material wherein a calcified hard tissue analogous to body hard tissue capable of making chemically a sufficient bond with body hard tissue is formed in a body within relatively short time passage.To attain the above-described objective, the hardening material for medical and dental use relating to the present invention is composed of a calcium phosphate powder and a hardening liquid and also of at least either one of collagen and/or collagen derivatives in a state of powder or solution, and the calcium phosphate powder contains a powder of .alpha.-tricalcium phosphate [.alpha.-Ca.sub.3 (PO.sub.4).sub.2 ]and/or tetracalcium phosphate [Ca.sub.4 (PO.sub.4).sub.2 O] as an essential component and the hardening liquid comprises at least one acid selected from inorganic acids and acetic acid.

Abstract: A method of fabricating an undoped or impurity-doped semi-insulating GaAs single crystal with the use of a silica boat comprises the steps of making a melt of GaAs in the silica boat except for a seed crystal, doping the melt with oxygen, maintaining the doped melt as it is for a predetermined period of time, solidifying the melt from the side opposite the seed crystal toward the seed crystal, seeding the melt when the melt attains a predetermined melt zone width on the seed crystal side, and moving the melt zone in the direction opposite the seed crystal for its solidification while keeping the melt zone width unchanged.