No abstract

The DX centre was observed on Mocvo-grown unintentionally doped AI,,,Ga,,,As by means of the Hall effect involving persistent photoconductivity (PPC), temperature-dependent photoluminescence (PL) and deep-level transient spectroscopy (DLTS). The ionisation energies of the hydrogen-like shallow donor (E: = 23 meV) and of the deep donor (Etd = 120 meV) with regard to the minimum were observed simultaneously by PL investigations at T = 75 K. The value E:d observed from the difference between the DLTS emission and capture barrier agrees excellently with that found by PL studies. The PL emission due to the transition involving the occupied DX centre was observed in a narrow temperature range (70 T 6 140 K). The population of the DX centre by thermally activated electrons which surmount the occupation barrier at these temperatures is indicated by the drop of the PPC and the DLTS capture studies. For the capture activation energy of the deep donor we obtain a value of 240 meV.

We have studied AlGaAs grown by molecular beam epitaxy (MBE) before and after post-growth hydrogen plasma treatment by means of temperaturedependent photoluminescence (PL), capacitance-voltage (cN), and electron-beaminduced current (EBIC) analysis. The excitonic and extrinsic luminescence features V I ,,-,ypc n,uan5 >a,,,p,c-D"",ec,eu LY a "yU1uyrll p'"""'" I r Y r a , L l l r neutralization effect of vacancies and shallow acceptors. The hydrogen incorporation provides an increase of t h e non-radiative lifetime of the minority carriers. This behaviour was checked by investigations of the minority carrier diffusion and of the quantum yield, which increase due to the hydrogen incorporation. The increase of the non-radiative lifetime is probably caused by t h e

The barrier height EB of a graded heterojunction as a function of the position is determined from photocurrent, Iph, and capacitance–voltage measurements on LPE grown anisotype heterostructures. The reliability of a theoretic relation obtained between Iph and EB is confirmed investigating the temperature dependence Iph(T). Using the capacitance and photocurrent–voltage measurements the dependence EB(W) (W width of the space charge region) is concluded. As a result, a heterotransition graduated in the range of about 150 nm with an averaged gradient ΔEB/Δz = 1 mV/nm is obtained. However, the barrier height is a complicated function of the position.

In 1.35 μm‐InGaAsP/InP DHS mesastructure diodes with differently spaced p‐n and heterojunctions the electron‐beam induced current and cathodoluminescence, the C–U characteristics, the DLTS, and the photoresponse as well as the injection luminescence as functions of the wavelength, temperature, and time are measured. The InP‐interlayer lying between p‐n and heterojunction supresses the collection of the photogenerated holes by means of the valence‐band offset induced pile‐up effect at low illumination levels and low temperatures, delays the motion of the holes during the collection at high illumination levels and reduces the hole injection into the n‐type quaternary active layer at low temperatures. Probably due to the separation of the p‐n junction from the active layer the content of nonradiative recombination centres in the active layer is reduced.