Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. For example, from the very beginning, the thickness of the solar cells is around 300 μm. Up to now, the most recent thin film based solar cell is developed to just around 5 μm, while the efficiency keeps the same. The method to reduce the volume of the semiconductor materials could be grinding, chemical etching or thin film lift-off by stress defoliation. Up to now, the thin film lift-off by stress defoliation is among one of the most famous method, since the material substrate can be recycled after the thin film lift-off. By using the thin film lift-off method, materials less than 100 nm thick can be obtained, this ultrathin semiconductor material holds great promise for developing high operation speed, mechanically flexible yet still high detection efficiency photon detection devices. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <100 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Simple calculation can show 100 nm silicon thin film absorption over the near-infrared spectrum (from 700 nm to 1000 nm) is less than 5%. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. The thin film lift-off using stress defoliation cannot be easily applied to ultrathin semiconductor materials since it is too fragile under stress. This work introduces a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. The semiconductor thin films are obtained from semiconductor-on-insulator wafers by the method of wet etching undercut and membrane release. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. These single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity. The spectral selectivity can be further exploited to develop a chip-scale, broadband spectrometer for hyperspectral imaging/sensing purposes. Later, we focus the discussion on the singe-photon avalanche photodetector using micron-meter thin semiconductor membrane. By using this ultrathin semiconductor membrane, the single photon detector we developed can be mechanically flexible. To make a brief conclusion, the ultrathin semiconductor membrane can be used for efficient imaging/sensing purpose. The purpose can vary in different condition, whether it is for wavelength selective, hyper-spectral sensing or single-photon level imaging.