Liangqing Zhu

Backside-illuminated infrared photoluminescence and photoreflectance: Probe of vertical nonuniformity of HgCdTe on GaAs

Vertical uniformity of HgCdTe epilayer is a crucial parameter for infrared detector engineering. In this work, backside illuminated infrared photoluminescence (PL) and photoreflectance (PR) measurements are carried out on an arsenic-doped Hg1−xCdxTe layer molecular-beam epitaxially grown on GaAs substrate, and the alloy composition and impurity states of the HgCdTe near the substrate are evaluated. By comparing to frontside illuminated PL and PR data, the vertical nonuniformity of composition and impurity states are evidenced. The results indicate that backside illuminated PL and PR are good pathway for evaluating contactlessly the nonuniformity of alloy composition and impurity states along the growth direction.

Competition of compressive strain with substrate misorientation in CuPt-type ordered GaInP/AlGaInP quantum wells

Temperature-dependent photoluminescence (PL) measurements are carried out on lattice-matched and compressively strained GaxIn1−xP/(Al0.66Ga0.34)yIn1−yP quantum wells (QWs) with CuPt-type long-range (LR) ordering. Experimental data show that compressive strain and substrate misorientation of the QWs affect the degree of LR ordering. The compressive strain competes with the misorientation of 6° off toward [111]A (denoted as 6 °A) significantly. It not only affects the distribution of domains with different degree of LR ordering in the x−y plane but also introduces fluctuation of the degree of LR ordering along the z direction of the QWs, which in turn causes the splitting of PL peaks. A phenomenological model is proposed to account for the experimental phenomena based on the principle of minimum total free energy. The results suggest that 6 °A misorientation should not be preferable for compressively strained GaxIn1−xP QWs with LR ordering.

Midinfrared Photoluminescence up to 290 K Reveals Radiative Mechanisms and Substrate Doping-Type Effects of InAs Nanowires

Photoluminescence (PL) as a conventional yet powerful optical spectroscopy may provide crucial insight into the mechanism of carrier recombination and bandedge structure in semiconductors. In this study, mid-infrared PL measurements on vertically aligned InAs nanowires (NWs) are realized for the first time in a wide temperature range of up to 290 K, by which the radiative recombinations are clarified in the NWs grown on n- and p-type Si substrates, respectively. A dominant PL feature is identified to be from the type-II optical transition across the interfaces between the zinc-blend (ZB) and the wurtzite (WZ) InAs, a lower-energy feature at low temperatures is ascribed to impurity-related transition, and a higher-energy feature at high temperatures originates in the interband transition of the WZ InAs being activated by thermal-induced electron transfer. The optical properties of the ZB-on-WZ and WZ-on-ZB interfaces are asymmetric, and stronger nonradiative recombination and weaker carrier-phonon interaction show up in the NWs on p-type substrate in which built-in electric field forms and leads to carrier assembling around the WZ-on-ZB interface. The results indicate that wide temperature-range infrared PL analysis can serve as efficient vehicle for clarifying optical properties and bandedge processes of the crystal-phase interfaces in vertically aligned InAs NWs.

Infrared photoreflectance investigation of resonant levels and band edge structure in InSb

Temperature-dependent infrared photoreflectance (PR) is employed on InSb for clarifying resonant levels (RLs) and band edge structure. Abundant PR features are well resolved around the bandgap and are verified to be of electronic inter-level transitions rather than the Franz-Keldysh oscillations. The evolution of the critical energies with temperature reveals the nature of the PR processes, from which one acceptor RL, two donor RLs, and a shallow acceptor level are quantitatively identified, and a detailed band edge structure is derived. The results show that temperature-dependent infrared PR analysis can serve as an efficient vehicle for clarifying both bound and resonant levels in semiconductors.

Photoionization absorption and zero-field spin splitting of acceptor-bound magnetic polaron in p-type Hg1-xMnxTe single crystals

Temperature-dependent magnetic (2–300 K), DC Hall (10–300 K), and infrared transmission (11.5–300 K) measurements are performed on a series of p-type Hg1-xMnxTe (0.12 ≤ x ≤ 0.26) single crystals in the spin-glass regime. Photoionization absorption (PIA) of acceptor-bound magnetic polarons (acceptor-BMPs) is observed to evolve with temperature, which is better accounted for by the classical oscillator model than by the quantum defect method. At low temperatures, p-type Hg1−xMnxTe manifests distinct phenomena of paramagnetic enhancement, negative magnetoresistance, and decrease of the effective binding energy and blueshift of the PIA of the acceptor-BMPs with nearly the same degree as temperature declines. A spin-splitting model is proposed, which can well reproduce the experimentally observed zero-field spin splitting of the acceptor-BMP level at low temperatures and the increase of the spin splitting as temperature drops. The results suggest that the acceptor-BMPs in Hg1−xMnxTe may have potential applicat...

Negative thermal quenching of below-bandgap photoluminescence in InPBi

This paper reports a temperature-dependent (10–280 K) photoluminescence (PL) study of below-bandgap electron-hole recombinations and anomalous negative thermal quenching of PL intensity in InP1–xBix (x = 0.019 and 0.023). Four PL features are well resolved by curve-fitting of the PL spectra, of which the energies exhibit different temperature dependence. The integral intensities of the two high-energy features diminish monotonically as temperature rises up, while those of the two low-energy features decrease below but increase anomalously above 180 K. A phenomenological model is established that the residual electrons in the final state of the PL transition transfer into nonradiative state via thermal hopping, and the thermal hopping produces in parallel holes in the final state and hence enhances the radiative recombination significantly. A reasonable interpretation of the PL processes in InPBi is achieved, and the activation energies of the PL quenching and thermal hopping are deduced.

Influence of local magnetization on acceptor-bound complex state in Hg1−xMnxTe single crystals

We performed temperature-dependent magnetic measurements and infrared photoluminescence (PL) measurements in various geometries on a series of p-type Hg1–xMnxTe single crystals ( 0.20≤x≤0.26). Evolution of PL features was observed, and zero-field spin splitting was identified for the acceptor-bound magnetic polaron (A0BMP). The results show direct evidence for local spontaneous magnetization of the A0BMP. Comparison with the Ditel–Spalek model indicates that besides the fluctuation and collective regimes, the A0BMP exhibits a new regime at low temperatures owing to the formation of the spin-glass state in Hg1−xMnxTe. The dissociation energy of the exciton bound to the A0BMP ((A0,X)BMP) varied rapidly with temperature, and the ratio of the dissociation energy of the (A0,X)BMP to the binding energy of the A0BMP was larger than the classical value of the A0X and no longer a constant, which breaks the Haynes rule. The free exciton localization process helps enhance the local magnetization of the (A0,X)BMP by ...

GaInSb/InAs/AlSb quantum wells with InSb- and GaAs-like interfaces investigated by temperature- and magnetic field-dependent photoluminescence

GaInSb/InAs/AlSb quantum wells (QWs) with typical InSb- and GaAs-like interfaces (IFs) are investigated by temperature- and magnetic field-dependent photoluminescence (PL), respectively. The results show that (i) as temperature rises the PL energy of the QWs with either InSb- or GaAs-like IFs blueshifts slightly below 50 K but redshifts above and broadens rapidly, and the mechanism behind this is correlated to the IF roughness-related layer thickness fluctuation equivalent to a localization energy of about 9.5 meV; (ii) the PL diminishes monotonously as magnetic field rises except for the delocalized PL process of the InSb-like IF QWs, and the magnetic field-induced PL quenching is attributed to the IF roughness-induced electron-hole separation in the type-II QWs; and (iii) the magnetic field-dependent PL energy follows a typical excitonic diamagnetic shift for both located and dislocated states, and the deduced exciton binding energy, reduced effective mass, and average wavefunction extent are insensitiv...