Modulation mechanism of infrared photoreflectance in narrow-gap HgCdTe epilayers: A pump power dependent study

Modulation of built-in surface electric field was well established as a mechanism of photoreflectance (PR) processes in bulklike semiconductors, though pump light induced excess carrier concentration was once suggested theoretically as another possibility. In this work, pump power dependent infrared PR measurements were carried out on two arsenic-doped narrow-gap HgCdTe epilayer samples in a wide power range from about 1 mW to up to 480 mW. The relation between the integral intensity I of main PR features and pump power P can be described with I ∝ P^k, and the k is sensitive to temperature and pump power. While it takes a value of about 0.5 at 11 K or under considerably high pumping power at 77 and 150 K, it is close to 1.0 in a low pump power range at 77 and 150 K. The modulation mechanism is indicated as a combination of the modulation of built-in surface electric field and the pumping induced excess carrier concentration near the band edge. The modulation of built-in surface electric field takes place when the Debye screening length is larger than the pump light penetration depth, otherwise the pumping induced excess carrier concentration also comes into force. High pump power significantly enhances the signal and improves the signal-to-noise ratio of PR spectrum especially when the pumping induced excess carrier concentration plays a dominant role and can, therefore, serve as a primary choice for performing infrared PR measurements on narrow-gap HgCdTe epilayers efficiently.