NSM Archive - Gallium Nitride (GaN) - Impurities and defects

Impurities and defects

Donors
Acceptors
Luminescence peak energies E_peak
Deep defect states
Binding energies of acceptors

Donors

Undoped GaN is n-type with electron concentrations n >= 10¹⁷cm^-3. The dominant donor is believed to be the nitrogen vacancy [Pankove et al.(1975)]. The binding energy of this donor is subject to large controversy. Values given range from 42(l)meV [Dingle & Ilegems (1971)] over 29(6)meV [Lagerstedt & Monemar (1974)] to 17meV [Vavilov et al.(1979)]. A deep donor level with E_d >;=10 meV is also postulated [Vavilov et al.(1979)]. No detailed information exists about the identity of these donors.

Acceptors

Most data have been derived from photoluminescence peaks which are caused by the recombination of free or bound electrons with bound holes.

Luminescence peak energies E_peak

Impurity	E_peak	Remarks	Referens
Li	2.23 eV	77 K; photoluminescence	Pankove et al.(1973)
Be or V_Ga	3.264 eV	4.2 K	Ilegems & Dingle (1973)
Be-complex or Be_Ga	2.36 eV		Monemar, Lagerstedt & Gislanson (1980)
Mg or V_Ga	3.264 eV		Ilegems & Dingle (1973)
Mg-complex or Mg_Ga	2.95 eV		Ilegems & Dingle (1973) Monemar, Lagerstedt & Gislanson (1980)
Dy	3.15 eV	77 K	Pankove et al.(1973)
Cd or V_Ga	3.268 eV 3.263	4.2 K 1.6 K	Monemar, Lagerstedt & Gislanson (1980); Lagerstedt & Monemar (1974)
Cd-complex or Cd_Ga	2.7 eV		Monemar, Lagerstedt & Gislanson (1980)
Zn or V_Ga	3.268 eV	4.2 K	Monemar, Lagerstedt & Gislanson (1980)
Zn-complex or Zn_Ga (A-band)	2.9 eV		Lagerstedt & Monemar (1974); Monemar, Lagerstedt & Gislanson (1980)
Zn_N (?) (B-band)	2.6 eV		Monemar, Lagerstedt & Gislanson (1980)
Zn^-_N (?) (C-band)	2.2 eV		Monemar, Lagerstedt & Gislanson (1980)
Zn^2-_N (?) (D-band)	1.8 eV		Monemar, Lagerstedt & Gislanson (1980)

Deep defect states

Undoped GaN is invariably n-type usually with a high free electron concentration (10¹⁷ ÷ 10¹⁸ cm^-3) at room temperature. Although the dominant donor has not been unambiguously identified there is a consensus that it is an intrinsic defect and most probably the nitrogen vacancy [Pankove et al.(1975)]. Energies are reported ranging from 17meV [Vavilov et al.(1979)] to 42meV [Dingle & Ilegems (1971)]. The resistivity of the material can be increased dramatically by the addition of group II atoms; these elements introduce deep acceptors which compensate the native donors. The same binding energy of 225 meV is reported [Lagerstedt & Monemar (1974)] for the addition of Zn, Cd, Mg, and Be, however it seems unlikely that these four dissimilar species would be identical and consequently it has been proposed that the acceptor is actually V_Ga [Monemar, Lagerstedt & Gislanson (1980)]. The vacancy concentration is believed to be increased by the presence of the group II element.

Binding energies of acceptors