Light emitting device and light emitting device module

A light emitting device comprising a substrate transparent at the emission wavelength and an active layer structure formed on such substrate, in which a layer for suppressing spectral-intensity-modulation due to the substrate-mode is provided between said substrate and said active layer structure, and further comprising:

• a first-conduction-type clad layer having the same conduction type with said substrate and formed between said substrate and said active layer structure;
• and
• a first-conduction-type, low-refractive-index layer formed between said substrate and said first-conduction-type clad layer,
• wherein a relation expressed by the following inequality is satisfied:
• nsub>nclad1>nLIL1 (inequality 1)
• where nsub represents the refractive index at the emission wavelength of said substrate, nclad1 represents the real part of an average refractive index at the emission wavelength of said first-conduction-type clad layer, and nLIL1 represents the average refractive index at the emission wavelength of said first-conduction-type, low-refractive-index layer.