A. D. Prins

High pressure determination of AlGaInP band structure

Abstract Low temperature photoluminescence measurements have been carried out at hydrostatic pressures up to 80 kbar to determine the band structure of the disordered ( Al x Ga 1 − x ) 0.5 In 0.5 P alloy system. Using a series of specifically designed samples we have measured how the Γ, L and X conduction band energies vary with strain and aluminium content. The direct band gap varies linearly from that of GaInP at a rate of 0.61 x eV. The position of the X minimum in GaInP is found to be 280 meV above the Γ, increasing linearly with aluminium content at a rate of 0.085 x eV. Measurements of unstrained and 1% compressively strained GaInP put lower limits on the Γ c -L c separation of 125 meV and 175 meV, respectively.

Investigation of the band structure of the strained systems InGaAs/GaAs and InGaAs by high-pressure photoluminescence

InxGa1-xAs quantum wells grown pseudomorphically in GaAs and AlGaAs with values ofx up to 0.25 have been studied by photoluminescence under high hydrostatic pressure. We concentrate here on the pressure range where the emissions quench and take on the characteristics of theX-minima. In the InGaAs/GaAs structures, these transitions display an unexpected pressure coefficient, -2.6 meV/kbar, twice that of theX minima in GaAs. We assign these transitions to theX minima in the wells, and therefore make a direct measurement of the strainedX positions as a function of composition. In the InGaAs/AIGaAs structures the crossovers occur against theX-minima in the barriers and these crossovers yield an accurate value for the band offset ratio for InGaAs/GaAs heterojunctions which is found to be 60:40 (CB:VB).

LED Junction Temperature Measurement Using Generated Photocurrent

LED-based lamps that are currently on the market are expensive due to the complex packaging required to dissipate the heat generated. This also limits their performance and lifetime due to the degradation of the phosphor or individual LED chips, in the case of RGB sources. There is a strong commercial imperative to develop in situ technology to measure and ultimately compensate for the thermal environment of a luminaire.

Direct measurement of band offsets in GaInP/AlGaInP using high pressure

High pressure photoluminescence experiments carried out at 2 K in the diamond anvil cell have been used to determine band offsets in GaInP/AlGaInP as functions of aluminium content and strain. We have used accurate measurements of the positions of the conduction band Γ and X minima to design samples specifically for high pressure experiments in which we have measured the band offsets. In the case of unstrained GaInP/(Al x Ga 1-x ) 0.5 In 0.5 P we obtain a value for the conduction b-and offset (ΔE c ) of ΔE c =0.73 ΔE g independent of x. We have also measured samples in which the erects of aluminium content and strain are combined (typical of many laser devices). A 1% compressively strained quantum well in (Al 0.3 Ga 0.7 ) 0.5 In 0.5 P barriers gives ΔE c =0.7±0.07ΔE g

Evidence for a defect level above the conduction band edge of InAs/InAsSb type-II superlattices for applications in efficient infrared photodetectors

We report pressure-dependent photoluminescence (PL) experiments under hydrostatic pressures up to 2.16 GPa on a mid-wave infrared InAs/InAs0.86Sb0.14 type-II superlattice (T2SL) structure at different pump laser excitation powers and sample temperatures. The pressure coefficient of the T2SL transition was found to be 93 ± 2 meV·GPa−1. The integrated PL intensity increases with pressure up to 1.9 GPa then quenches rapidly indicating a pressure induced level crossing with the conduction band states at ∼2 GPa. Analysis of the PL intensity as a function of excitation power at 0, 0.42, 1.87, and 2.16 GPa shows a clear change in the dominant photo-generated carrier recombination mechanism from radiative to defect related. From these data, evidence for a defect level situated at 0.18 ± 0.01 eV above the conduction band edge of InAs at ambient pressure is presented. This assumes a pressure-dependent energy shift of −11 meV·GPa−1 for the valence band edge and that the defect level is insensitive to pressure, both ...

Laminated gaskets for absorption and electrical measurements in the diamond anvil cell

We have developed gaskets laminated from two layers of steel both for optical absorption and for electrical measurements in the diamond anvil cell. For absorption, these gaskets provide masking around the sample, avoiding the need for imaging of the gasket hole. For electrical measurements, laminated gaskets avoid the need for specially prepared diamonds as the feedthrough wires are not in contact with the anvils. Using argon as a pressure medium, both techniques have been used up to about 50 kbar at 300 and at 10 K.

The pressure dependence of the valence band discontinuity in quantum well structures

The use of hydrostatic pressure to determine the valence and conduction band offsets and their pressure dependence in both Type I and Type II quantum well structures will be described. Recent exper...

Diamond anvil cell high-pressure techniques for semiconductor research

A miniature diamond anvil cell high-pressure system is described, together with loading, operating and experimental methods, making high pressure in the 100 kbar range an accessible and portable technique. Some applications are discussed.

CdTe/ZnTe strained layer superlattices under high pressure

Abstract Photoluminescence due to light and heavy holes in CdTe/ZnTe strained layer superlattices has been studied under pressure in a diamond anvil cell. Two bands are observed and their pressure dependence fits with envelope function theory. One band is quenched at 4GPa and this gives 75meV for the valence band offset. The other band is observed up to 30kbar above the phase transition pressure of CdTe. This superpressing is explained by the inhibition of phase transitions in an (001) oriented superlattice.

Bulk moduli of GaInAsP and GaInAs by photoluminescence up to 100 kbar

High-pressure photoluminescence measurements in the diamond anvil cell have allowed accurate spectroscopic measurements of the bulk moduli of GaInAsP and GaInAs lattice-matched epitaxial layers relative to the modulus of their InP substrates. GaInAsP is found to be the same as InP to within 1%, in agreement with empirical rules, while the value for GaInAs is 5% lower.