Photocapacitance study of bulk deep levels in ZnSe grown by molecular-beam epitaxy

Abstract

The influence of initial growth conditions and lattice matching on the deep level spectrum of n-ZnSe grown on GaAs by molecular-beam epitaxy is investigated by means of deep level optical spectroscopy. A detailed study of both the steady-state and transient photocapacitance allows us to measure optical threshold energies, concentrations, and emission rates of electronically active defects in the ZnSe layer. Several deep levels are found in the ZnSe layer at Ec−Et=1.15, 1.46, 1.90, and 2.25 eV with concentrations in the 1012–1014 cm−3 range. When a 2-nm-thick composition controlled interface layer is grown at different beam pressure ratios prior to the ZnSe growth, a distinct decrease in the 1.46 eV level concentration with increasing Se content is found. Deposition of a lattice-matched InxGa1−xAs buffer layer prior to the ZnSe growth reduces the concentration of both the 1.15 and 1.46 eV levels by over an order of magnitude, indicating the role of lattice matching in the ZnSe overlayer. We also perform depth profiling of the defect distributions within the ZnSe overlayer to see the effect of the ZnSe thickness on the concentration of these levels as well as their possible association to the ZnSe/GaAs interface. We find that only the 2.25 eV level concentration shows a dependence on depth, increasing as the II–VI/III–V interface is approached.

Role of subsurface defects in metal-ZnO(0001¯) Schottky barrier formation

“…14,15 We performed current-voltage ͑I-V͒ measurements following DRCLS studies using a HP 4145B semiconductor analyzer. Capacitance-voltage ͑C-V͒, deep level transient spectroscopy ͑DLTS͒ measurements, and deep level optical spectroscopy ͑DLOS͒, as described elsewhere, 16 were performed on Schottky diodes. DRCLS spectra were taken using a JEOL 7800F ultrahigh vacuum ͑UHV͒ scanning electron microscope ͑SEM͒ ͓Fig.…”

Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN∕GaN heterostructures using capacitance deep level optical spectroscopy

“…Comprehensive discussion of DLOS is available elsewhere. 10 Figure 1͑a͒ displays the SSPC at V G = 0, −3.6, and −4 V. Unlike typical capacitance spectroscopy of uniformly doped bulk films, the increase in photocapacitance relative to the equilibrium value ⌬C / C 0 is not proportional to the areal deep level density D t ; consideration of D t is given later. Considering the V G = 0 V spectrum, which can sense deep levels within both the AlGaN and GaN layers, several important features are apparent.…”

Photocapacitance study of deep levels in thin CdTe PV devices

“…The positive changes in the capacitance signal for these three peaks are indicated for clarity. The sharp positive changes in the capacitance signal are apparent optical transitions for the emission of holes and indicate a donor type level given the p-type material and the initial trap occupancy p (0) = N t [8,15,16]. The negative changes may be optical transitions for electrons or the decrease in the cross section for holes and as such are ambiguous [15].…”

“…Steady state PHCAP spectra also contain information on the trap densities N t [8,16] that is often presented as…”