1. Field of the Invention
The present invention relates to a process for crystal growth of III-V group compound semiconductor containing a compound semiconductor crystal layer of high electric resistance.
2. Description of the Related Art
Electronic devices using a compound semiconductor must have an electric resistance between elements as large as possible in order to prevent a malfunction and a breakdown caused by leakage current between elements.
Progress in integration degree, however, makes narrower the distance between electronic elements and consequently the electric leakage tends to occur between the elements.
Reliable insulation (isolation) between elements can achieve high performance and high integration simultaneously. Therefore, it has been desired strongly to develop a process for growing a compound semiconductor crystal layer enabling such reliable insulation between elements.
To satisfy the above desire, it has been conducted to grow a crystal layer of high electric resistance by crystal growth using molecular beam epitaxy (hereinafter referred to as MBE, in some cases), metal organic chemical vapor deposition (hereinafter referred to as MOCVD, in some cases) or the like.
The processes employed conventionally to grow a crystal layer of high electric resistance include a process of doping an AlGsAs layer with a dopant such as oxygen, a transition metal or the like. It is known that oxygen or a transition metal forms a deep level in the forbidden band of a semiconductor. Therefore, by forming a deep level of said element in a large amount in an Al-containing crystal by utilizing the high activity of Al to said element, a crystal layer of high electric resistance can be grown in said crystal. As the specific processes to grow a crystal layer of high electric resistance, there are known, for example, a process using oxygen gas as an oxygen dopant; a process using, as an oxygen dopant, an organometallic compound having an aluminum atom-oxygen atom direct bond [Japanese Patent Application Kokai (Laid-Open) No. 1-220432]; and a process using, as a dopant, an organometallic compound having an aluminum atom-oxygen atom direct bond or an organometallic compound containing a transition metal [Japanese Patent Application Kokai (Laid-Open) No. 3-22519].
However, when oxygen gas is used as a dopant, oxygen tends to remain in the reaction furnace owing to the high reactivity, which may invite the oxygen incorporation into the upper crystal layer right on the high resistance layer and the consequent deterioration of crystal quality. Hereinafter, that "oxygen tends to remain" is referred to as "a large effect of oxygen remaining" and that "oxygen is unlikely to remain" is referred to as "a small effect of oxygen remaining", in some cases.
When an organometallic compound having an aluminum atom-oxygen atom direct bond is used as an oxygen dopant, there has been a problem that oxygen concentration and aluminum concentration cannot be controlled independently. Further, since the organo-metallic compound generally contains a dimer and a trimer each having a vapor pressure different from that of the monomer, there has also been a problem that the vaporization behavior of the compound is unstable and it is impossible to obtain a given oxygen concentration continuously.
An object of the present invention is to provide a process for growing a compound semiconductor crystal layer having a high electric resistance, by the use of a dopant which enables the independent controls of oxygen concentration and aluminum concentration and which has a small effect of oxygen remaining.