skip to main content

Title: Effect of uniaxial stress on gallium, beryllium, and copper-doped germanium hole population inversion lasers

The effects of stress on germanium lasers doped with single, double, and triple acceptors have been investigated. The results can be explained quantitatively with theoretical calculations and can be attributed to specific changes in the energy levels of acceptors in germanium under stress. In contrast to previous measurements, gallium-doped Ge crystals show a decrease in lasing upon uniaxial stress. The decrease seen here is attributed to the decrease in heavy hole effective mass upon application of uniaxial stress, which results in a decreased population inversion. The discrepancy between this work and previous studies can be explained with the low compensation level of the material used here. Because the amount of ionized impurity scattering in low-compensated germanium lasers is small to begin with, the reduction in scattering with uniaxial stress does not play a significant role in changing the laser operation. Beryllium-doped germanium lasers operate based on a different mechanism of population inversion. In this material it is proposed that holes can transfer between bands by giving their energy to a neutral beryllium atom, raising the hole from the ground to a bound excited state. The free hole will then return to zero energy with some probability of entering the othermore » band. The minimum and maximum E/B ratios for lasing change with uniaxial stress because of the change in effective mass and bound excited state energy. These limits have been calculated for the case of 300 bar [100] stress, and match very well with the observed data. This adds further credence to the proposed mechanism for population inversion in this material. In contrast to Be and Ga-doped lasers, copper-doped lasers under uniaxial stress show an increase in the range of E and B where lasing is seen. To understand this change the theoretical limits for population inversion based on both the optical phonon mechanism and the neutral acceptor mechanism have been calculated. The data are described by population inversion via optical phonons at zero pressure. However, both mechanisms most likely occur when the slightly higher, non-uniform pressures of 300 bar are applied, leading to an increase in population inversion and lasing. Upon further increasing the pressure to 600 bar, the limits for population inversion decrease and a decrease in the lasing is seen.« less
Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
674711
Report Number(s):
LBNL--41854
ON: DE98056112; TRN: AHC29820%%165
DOE Contract Number:
AC03-76SF00098
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: DN: Thesis submitted to Univ. of California, Berkeley, CA (US); TH: Thesis (M.S.); PBD: May 1998
Research Org:
Lawrence Berkeley National Lab., Materials Sciences Div., Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Energy Research (ER); Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; SEMICONDUCTOR LASERS; LASER MATERIALS; POPULATION INVERSION; GERMANIUM; FAR INFRARED RADIATION; DOPED MATERIALS; STRESSES; GALLIUM; BERYLLIUM; COPPER; HOLES