Photothermal Ionization Spectroscopy of Mercury Vacancies in HgCdTe Epitaxial Films

Photoconductivity spectroscopy of arsenic-related acceptors in HgCdTe

“…The appearance of narrow lines in the PC spectrum is associated with the shallow excited states in the acceptor spectrum (0.42 meV and 1.1 meV for a neutral and singly ionized center, respectively). These particular states have a large matrix element for the optical transitions from the ground state because the fraction of the light hole subband in the expansion of the wave function is about 50%, while for other neighboring states it turns out to be not more than 10% [17]. In a qualitative analysis, these states can be viewed as the lower states (i.e.…”

“…For instance, if 1% Ge is added to the Si:B, the line pattern of the intracenter transitions disappears completely in the absorption spectrum for the boron impurity [15]. At the same time, PC lines associated with the photothermal ionization of the mercury vacancies were found in HgCdTe ternary alloys in recent works [16,17]. Although such lines are quite wide (∼3 meV) they indicate that the potential fluctuations in the material under study are fairly small.…”

Non-Radiative Transitions of Holes on Mercury Vacancies in Narrow-Gap HgCdTe

“…We applied Fermi's golden rule to calculate the possibility of hole transitions to various states of Hg vacancies during phonon emission. As the ionization energy of a neutral Hg vacancy (11 meV [16]) is lower than the energy of a transversal optical phonon (~15 meV [17]), only acoustic phonons can be involved in the hole capture by a singly charged center and in the non-radiative intracenter transitions of a neutral vacancy.…”

“…Note that for mercury vacancies, the observed ionization energies deviate from the results of calculations in the framework of the effective mass approximation [14,16]. Therefore, we calculated the hole energies and wave functions with the central cell potential (CCP) added to the acceptor field, as described in detail in Ref.…”

“…The PC spectra exhibited bands near 10 meV and 20 meV that were associated with the photoexcitation of neutral and singly ionized mercury vacancies, respectively. The shape of these PC bands and their quenching with temperature indicated that they are mainly formed due to the photothermal ionization of the vacancy, i.e., an optical transition to a shallow excited state followed by thermal excitation into the valence band continuum [16].…”