Photonic and quantum thermometry using active resonator compound semiconductor photonic integrated circuits

Semiconductors are extremely useful for temperature sensing owing to the strong temperature dependence of their optical and electronic properties. Silicon, the most widely used semiconductor, underpins modern electronics and is increasingly important in integrated photonics, offering a cost-effective platform for optical sensors. Silicon-based ring resonator (RR) temperature sensors operate via the temperature-dependent change in silicon's refractive index (dn/dT), which affects the optical modes in the ring. However, silicon has two main limitations: its indirect band gap makes it a poor light emitter, necessitating external light sources, and its thermal properties are fixed. In contrast, compound semiconductors, such as indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN) and indium arsenide (InAs), have direct band gaps, making them efficient light emitters as commonly used in light-emitting diodes and lasers. Their thermal properties can also be tailored through alloying. These features make them ideal for 'active resonator' temperature sensors with integrated light sources, allowing customization for various temperature ranges. This paper focuses on InP-based alloys, highlighting their fundamental properties and potential for integration into active quantum well-based heterostructures. These can be fabricated into micro-ring and other resonator designs. Integrating light sources within the sensor enhances both simplicity and functionality, paving the way for versatile temperature sensors suited to a wide range of applications. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.