The electron diffusion length in p‐type GaAs:Ge grown by liquid‐phase epitaxy has been measured as a function of hole concentration. The direct measurements were made by two different techniques —a laser beam scan on beveled samples and an α particle scan on cleaved samples. These measurements are in good agreement and show that the diffusion length increases from ∼6 μm at p=1×1019 cm−3 to ∼20 μm at p=7×1016 cm−3. In addition, the diffusion length was estimated from electroluminescent decay times of p‐n junctions and the values obtained were in reasonable agreement with those directly measured for the same materials.

Minority carrier diffusion length and recombination lifetime in GaAs:Ge prepared by liquid‐phase epitaxy

Microscopy using a scanning approach is reviewed, with numerous references to previous work, as at 1987, before the confocal laser scanning microscope was widely available commercially. The advantages of microscope imaging using a scanning technique are described. The principles of confocal microscopy are introduced. Use of Bessel beam illumination in a confocal microscope is discussed. This combination can increase spatial resolution while retaining some confocal optical sectioning. The advantages of imaging using a scanning method with a point source are detailed. For example, differential phase contrast may be performed to obtain phase information. Use of a point source allows different types of spectroscopy to be performed in a spatially resolved fashion. An advantage of point-source systems for such applications is that imaging, performed with the incident radiation, is separated from wavelength selection and analysis of the emitted radiation, thus simplifying system design and resulting in superior performance. Use of a point source to excite carriers in a semiconducting sample allows the electronic properties of materials and devices to be investigated. Advantages of object scanning, rather than beam scanning, are discussed. Advantages of using a laser source are described, including the use of the heterodyne technique as a synthetic confocal pinhole, and nonlinear microscopy such as two-photon fluorescence and CARS (coherent anti-Stokes Raman spectroscopy). It should be noted that 1987, as well as being before commercial confocal microscopes were widely available, was before the special properties of Bessel beams were appreciated, and before two photon fluorescence microscopy was first experimentally demonstrated.

Scanning Optical Microscopy

Properties and Applications of III–V Compound Films Deposited by Liquid Phase Epitaxy

Room‐temperature electron diffusion lengths (Ln) were determined for lattice matched, p‐type InGaAsP and InGaAs layers grown by liquid phase epitaxy on Sn‐doped (100)‐InP substrates by measuring the variation of the short‐circuit photocurrent as a focused laser beam was scanned along a beveled (ϑ∼1 °) p‐n junction. The hole concentrations, determined by capacitance‐voltage (C‐V) measurements, indicated an almost linear relationship between the hole concentrations in both the quaternary and ternary layers and the amount of Zn in the melt for the growth temperatures and substrate orientation used in this work. The electron diffusion lengths were longest at the lowest hole concentrations and decreased monotonically as the concentration increased. At the lowest doping levels, Ln was 3.5 μm at p = 3×1015 cm−3 for the quaternary and 2.5 μm at p = 1.4×1016 cm−3 for the ternary. At the highest hole concentration (p = 5×1018 cm−3) Ln was 0.13 and 0.83 μm for InGaAsP and InGaAs, respectively.

Room‐temperature electron diffusion lengths in liquid phase epitaxial InGaAsP and InGaAs

The optical microprobe is used to measure electron diffusion lengths in solution‐grown p‐type layers of Ge‐doped GaAs. They are found to be ∼ 20 μ, which gives an electron lifetime of ∼ 5×10−8 sec.

Electron diffusion length in solution‐grown GaAs : Ge

The minority‐carrier diffusion length on either side of a GaP p‐n junction have been determined from measurements of the short‐circuit current under uv excitation. The uv lines at 3.41 and 3.53 eV are extracted from an Ar laser and are focused to a spot 10 μ in diameter. The uv spot is scanned along the angle‐lapped surface of the junction to obtain the variation of short‐circuit current as a function of distance normal to the junction from which the diffusion length is derived. The technique provides a determination of diffusion lengths as short as 0.13 μ with an accuracy of 15%. The technique is straightforward and should be useful in the evaluation of GaP and other semiconductor material containing p‐n junctions.

C. J. Hwang

Papers

uv Microprobe Technique for Measurement of Minority‐Carrier Diffusion Length in GaP p‐n Junction Material