Electron and hole impact ionization coefficients in GaAs/Al0.45Ga0.55As/Al0.3Ga0.7As coupled well systems

Abstract

We have measured electron and hole multiplication factors and impact ionization coefficients in 550 Å GaAs/500 Å Al0.3Ga0.7As quantum wells with an intermediate Al0.45Ga0.55As barrier (50 and 100 Å) inserted in the well region. It is seen that while the measured value of α(E) is insensitive to the position of the intermediate barrier in the well, the value of β(E) is very sensitive. The value of α/β varies from less than unity to 5, depending on the position of this barrier. These results suggest that hole confinement and scattering play a major role in making the value of α/β greater than unity in these multilayered structures.

Avalanche noise characteristics of single Al/sub x/Ga/sub 1-x/As(0.3<x<0.6)-GaAs heterojunction APDs

“…4-6. The claims by Chin et al [2], and by others [3]- [7] that heterojunctions could be used in avalanche regions to reduce excess noise by tailoring the ratio via the band-edge discontinuity, have not been borne out [8]- [17]. Indeed, increasing the aluminum fraction above and hence band-edge discontinuity actually increases excess noise, as shown in Figs.…”

“…Choice of the layer heterostructure could therefore influence the value of which controls the degree of noisy feedback processes [1]. Subsequent experiments by numerous authors variously supported [3]- [7] or disagreed [8]- [15] with these predictions. However, the most compelling evidence comes from Chia et al [16], [17], who compared multiplication in both homojunction and single heterojunction Al Ga As-GaAs p -i-n diodes and found that the multiplication in heterojunction diodes, and hence the ionization coefficients, were not enhanced over those of corresponding homojunction diodes.…”

Other Major Properties Related to the Energy-Band Structure

“…The reduction in excess multiplication noise in the superlattice APD structure was experimentally demonstrated by Kagawa et al, 215 who also found that the electron ionization coefficient is enhanced Figure 10.32 Three Al^GaovAs/GaAs mulriple-quantum-well configurations having a thin Alo^GaojsAs barrier inside the GaAs well (on the left) and measured ionization coefficients (on the right): (a) type-A, (b) type-B, and (c) type-C devices. (From Bhattacharya et al 217 ) over the value in GaAs at an electric field of 2.5xl0 5 V/cm when the barrier material is of a direct-gap type (Al x Ga,. x As, x<0.45).…”

“…More recently, Bhattacharya et al 217 have measured the impact-ionization coefficients in A^GaojAs (500 A)/GaAs (550 A) quantum wells with an intermediate Al 045 Gao 55 As barrier (50 and 100 A) inserted in the well region. Their studied sample structures and measured results are shown in Fig.…”

“…10.32. 217 For the type-A device [(a)], a e is smaller than a h in the measured bias range, and the ratio a e /a h varies between 1 and 3. For the type-B device [(b)], a c is larger than a h , and the ratio aja h varies in the range 1-3.…”