Gallium nitride-based semiconductor element, optical device using the same, and image display apparatus using optical device

A gallium nitride-based semiconductor element comprising:

• a first GaN-based compound layer comprising:
• a first undoped GaN layer,
• an n-type conductive first GaN-based compound semiconductor layer formed on the undoped GaN layer,
• an underlayer formed directly on the n-type conductive first GaN-based compound semiconductor layer, and
• a second undoped GaN layer formed directly on the underlayer;
• an active layer formed on the second undoped GaN layer;
• and
• a second GaN-based compound layer including a p-type conductive layer formed on the active layer such that the active layer is provided between the first GaN-based compound layer and the second GaN-based compound layer,
• wherein the underlayer has an n-type impurity concentration in the range of 3×1018 to 3×1019/cm3, and when a reverse bias of 5 V is applied, a leakage current density, which is the density of a current flowing per unit area of the active layer, is 2×10−5 A/cm2 or less.