Near infrared intersubband transitions in delta-doped InAs/AlSb multi-quantum wells

Recently, the development of a compact light source operating in terahertz (THz) frequency range has attracted great amount of interest. Our goal is to realize all optical light sources pumped by a compact near infrared diode laser. For this purpose, we investigate intersubband transitions (ISBTs) in InAs/AlSb multiple quantum wells (MQWs). The family of semiconductors with a lattice constant of around 6.1 Å (InAs, AlSb, and GaSb) has several advantageous features such as the large conduction band discontinuity of about 2.1 eV and small effective mass in InAs leading to strong ISBTs. Previously, we studied the ISBTs in unintentionally doped InAs/AlSb for relatively wide wells and reported that no ISBTs were observed for well width less than 5 nm. Ohtani et al. reported ISBTs can be observed in narrower (2.7 nm) InAs/AlSb MQWs. In order to observe ISBTs in near infrared region, we investigate heavily doped InAs/AlSb MQWs with the well width, d, less than 5 nm.