p- GaN surface treatments for metal contacts

Abstract

The chemical bonding and electronic properties of wet, chemically treated p-GaN surfaces were studied using synchrotron radiation photoemission spectroscopy. Chlorine-based chemical bonding was identified on the conventional HCl-treated p-GaN surface, which is associated with a shift of the surface Fermi level toward the conduction band edge by ∼0.9 eV with respect to the thermally cleaned surface. Compared to the HCl-treated surface, the surface Fermi level on the KOH-treated surface lies about ∼1.0 eV closer to the valence band edge, resulting in a much smaller surface barrier height to p-type materials than the HCl-treated surface. The smaller surface barrier height to p-GaN after KOH treatment can lead to a lower contact resistivity and can play an important role in lowering the metal contact resistivity to p-GaN.

X-ray photoemission determination of the Schottky barrier height of metal contacts to n–GaN and p–GaN

“…3,4 The effect of these treatments on the surface chemistry was correlated with the electronic properties through monitoring changes in the movement of the Ga 3d core level. The KOH treatments led to a decreased Ga/N ratio on the surface for both n-and p-GaN.…”

“…Contacts to p-type GaN have been particularly challenging, since it is difficult to grow samples with a high enough carrier concentration to promote field emission through the Schottky barrier. Due to the complexity of metallurgical contacts, various approaches have been tried, including chemical surface treatments, [3][4][5][6][7] plasma cleaning, [8][9][10] metal deposition techniques ͑sputtering, electron beam, or thermal deposition͒, [11][12][13] contact annealing in a variety of ambients, 14,15 and use of bilayers 16 -18 or multilayers [19][20][21] of various metals.…”

n- GaN surface treatments for metal contacts studied via x-ray photoemission spectroscopy

“…3,4 Previously, we reported on the surface chemistry and electronic properties of HCl-and KOH-treated p-GaN samples. 5 For p-GaN it was found that the HCl treatment led to an increase in the Ga/N ratio ͑Table I͒ which corresponded to a higher relative surface barrier height. Conversely, KOH treatment decreases the Ga/N ratio, which corresponded to a lower relative surface barrier height.…”

Влияние обработки поверхности в BCl-=SUB=-3-=/SUB=- плазме на формирование омических контактов к структурам AlGaN/GaN

“…Такой сдвиг составляет 0.2 и 0.5 eV в случае обработки с напря-жениями смещения на подложке, равными 20 и 40 V соответственно. Сдвиг энергетического положения уров-ня Ga3d в сторону больших энергий связи может быть объяснен сдвигом поверхностного уровня Ферми (E F ) к дну зоны проводимости (E c ) [13]. Это, в свою очередь, свидетельствует об уменьшении высоты поверхностного барьера (E b ).…”