Photonic crystals (PCs) are a new class of artificial materials which consist in a periodic modulation of the dielectric constant in one, two, or three dimensions. This spatial periodicity of the dielectric function gives rise to a photonic band gap, a frequency interval of forbidden light propagation. PCs incorporating point or line defects may serve as building blocks in future photonic integrated circuits (PICs). Two-dimensional PCs based on a hexagonal pattern of air holes were deeply-etched in an InP/InGaAsP/InP heterostructure slab waveguide. Their spectral properties were assessed by optical transmission measurements. A systematic investigation of several types of 2D PC-based cavities and waveguides is performed. Resonances in the smallest point-defect structure, with one hole unetched, were observed with quality factors on the order of cavities in membrane photonic crystals. The mini stop-band (MSB), a dip in the transmission spectrum of a three-missing row PC waveguide, is also investigated. Tunable PC devices required for PIC applications can be realized by infiltrating the air holes with liquid crystals (LCs) which are characterized by a temperature-dependent index of refraction. A red shift of the PC transmission spectrum is observed after infiltration. Temperature tuning of the optical properties of these LC-filled PC devices is successfully demonstrated not only for cavities but also for the MSB. Thermally-induced red shifts of the H1-cavity resonance peak and of the MSB location are evaluated at approximately 7-8 nm.