THz intersubband absorption in n-type Si1−xGex parabolic quantum wells

Michele Montanari,Luciana Di Gaspare,Leonetta Baldassarre,Luca Persichetti,Monica De Seta,Michele Ortolani,Giacomo Scalari,David Stark,Giovanni Capellini,Chiara Ciano,Cedric Corley,Michele Virgilio

doi:10.1063/5.0048344

Abstract

High-quality n-type continuously graded Ge-rich Si1−xGex parabolic quantum wells with different doping levels were grown by using ultrahigh-vacuum chemical vapor deposition on Si(001) substrates. A thorough structural characterization study highlights an ideal parabolic compositional profile. THz intersubband absorption has been investigated in modulation-doped samples and samples directly doped in the wells. The comparison of experimental absorption data and theoretical calculations allowed us to quantify the impact of electron correlation effects on the absorption resonances in the different doping conditions and for electron sheet densities in the (1÷6)×1011 cm−2 range. A single optical resonance is present in modulation doped samples. Its peak energy and line shape are independent of temperature-induced variations of the electron distribution in the subbands up to 300 K, in agreement with the generalized Kohn theorem. This achievement represents a relevant step forward for the development of CMOS compatible optoelectronic devices in the THz spectral range, where thermal charge fluctuations play a key role.

Highlights

S (QWs) have been the focus of intense research in the last few decades due to their importance for optoelectronic devices, such as quantum cascade lasers[1,2,3] and quantum well photodetectors,[4,5] and the rich physics that can be investigated, like the strong and ultrastrong light-matter coupling.[6,7,8] In this context, parabolic quantum wells (PQWs) have been recently identified as a interesting quantum system.[9,10,11]
PQWs have been proposed[9] as promising candidates for the development of THz sources operating at room temperature, with relevant applications in several fields, ranging from biology, medicine, and security communications.[14]
The use of PQWs in optical microcavities allowed observation of strong light matter coupling at room temperature, where the thermal energy kT is larger than the photon energy,[15] and to reach the ultrastrong coupling regime.[10]

Summary

Introduction

S (QWs) have been the focus of intense research in the last few decades due to their importance for optoelectronic devices, such as quantum cascade lasers[1,2,3] and quantum well photodetectors,[4,5] and the rich physics that can be investigated, like the strong and ultrastrong light-matter coupling.[6,7,8] In this context, parabolic quantum wells (PQWs) have been recently identified as a interesting quantum system.[9,10,11]. In this Letter, we demonstrate the deposition of a stack of identical n-doped, continuously graded Ge-rich Si1ÀxGex PQWs. By exploring samples with different doping levels and doping geometry, we investigate ISB absorption spectra as a function of temperature, within the range from 10 K up to 300 K.

Results

Conclusion